Reviewed in the United States on March 26, 2020
The mouse comes in a box made of cardboard, with a wraparound, clear, plastic panel to display the mouse. Inside, you'll find the mouse, a USB charge cable (the same kind used for charging many smartphones) and an instruction booklet, all contained in a flexible plastic insert. The English prose in the booklet has plenty of amusing locutions often seen with off-brand, imported products (one quote: "Put the mouse stopped, after 3secs, enter first-order sleep mode."), but the diagrams are generally useful.
The Operation [sic] System section under System Requirements says "Suggest above Windows8.0 version". I suspect that any Windows-based computer that will work with a USB mouse - certainly Windows XP or higher - will work with this one via the included USB nano transceiver. However, computers running versions of Windows prior to 8.0 may not be able to support connecting the mouse via Bluetooth.
The first thing I did, out of habit, was look for a battery compartment -- but, of course, this mouse doesn't have a battery compartment, because it is powered by an internal battery (480mA/hour LiIon, according to the manual), so there is not user-accessible battery compartment. Instead, there is a USB charge port on the front edge of the mouse, so if your mouse doesn't work when you first turn it on, simply plug it into an available USB port on your computer, or into your cell phone charger (your cell phone most likely has an identical charge port, and the power requirements will be compatible) and charge it up. The next step is to turn the mouse on, using the power switch on its underside.
The manual says that the USB transceiver (referred to in the manual as a "USB nano receiver") is "in the box". While this is technically correct, in the sense that the whole set arrived in the box, you will not find the USB transceiver taped to the outer box or tucked into the plastic insert. The transceiver is, in fact, contained in a dedicated storage slot in the bottom of the mouse. That's good, from the standpoint of having someplace to put the transceiver if you decide to stop using the mouse. What's not good is that the transceiver is rather difficult to remove from the storage slot. It's not stuck tight, but there's something in there that seems to holding it in and resisting when I try to pull the transceiver out. Maybe someone with longer fingernails than mine could get it out without using a tool. I tried prying it out with one of my house keys, but was only able to get it partially out that way, and as soon as the key slipped, the transceiver dropped back into the storage slot. My next step would have been to try prying with a knife, but I decided instead to connect the mouse via Bluetooth, hoping this would be more idiot-resistant than using the USB transceiver.
Bluetooth pairing could be easier. If you'll be using the mouse with a Windows desktop computer, I recommend keeping a conventional, wired mouse connected to the computer until after you've successfully paired the LeadsaiL mouse, because it's hard to navigate Windows' Bluetooth dialog boxes without a mouse. In Windows 10, the first step is to make sure the computer's Bluetooth radio is turned on. Next, find the Bluetooth/2.4G button on the bottom of the mouse, and press and hold it for more than 3 seconds. The button should begin flashing rapidly, at which point the mouse is in pairing mode. After a short pause, the mouse should appear as "BT4.0+2.4G Mouse" in your list of Bluetooth devices, but it won't be ready to use yet. Your next step will be to click on the mouse in your Bluetooth devices list and click on it to pair. After your computer and mouse are paired, you'll need to click on the Connect button that appears with it in the Bluetooth list. After I did this, I experienced a long pause of 3 to 5 minutes before the mouse became responsive. I suspect that Windows was locating and loading drivers for the mouse, although I saw no indication of this on the screen.
USING THE MOUSE
Once connected, the mouse works pretty much as you'd expect. Most users should find that it fits nicely in the hand, with the fingers resting naturally on the buttons. The mouse sensitivity seems to be about the same as any other mouse I've used, and the left and right buttons and scroll wheel work as expected. The only exception is that a press on the scroll wheel, on most mice with scroll wheels, mimics a press on the left mouse button. On this mouse, the scroll wheel makes an audible, tactile click when you press it, but doing so doesn't trigger any action on the computer. (There may be some software you can download that will let you program the scroll wheel on this mouse.) The mouse is billed as "silent". Moving it is certainly silent; clicks on the right and left mouse buttons are quiet enough that you'd have to put your ear right next to the mouse to hear them, but I wouldn't call them silent.
The DPI button is basically a shorthand, 3-setting version of the mouse sensitivity slider in Windows' (and probably MacOS') mouse options. It switches among three sensitivity settings in a round robin fashion. There is a green indicator light right next to it that flashes once, twice or three times when you press the button to indicate which setting your press on the button has just activated.
The mouse also has two buttons on its left side, where most users' thumbs rest. Those buttons do nothing unless you have a game or other application that uses them. I did not have any such application with which to test them.
The mouse's power saving (sleep) functions don't seem to work exactly as described in the manual, at least on Windows 10 computers. My observation is that as long as Windows is up and running, simply moving the mouse takes it out of what the manual calls first-order sleep mode. If you leave the mouse untouched for more than half an hour or so, it goes into "secondary sleep mode", which, according to the manual, turns off the mouse's Bluetooth radio. That had me a bit concerned, but it turns out that a click on one of the mouse buttons wakes the mouse back up, and after that, the mouse reconnects to my computer automatically, and quickly enough that I'm not tempted to start troubleshooting.
The main downside to connecting the mouse to a Windows computer via Bluetooth is that the mouse doesn't function until Windows is fully booted, sometime after the logon screen appears. At that point, you need to click a mouse button to wake it up, which may be a bit disconcerting to some users at first. However, I don't believe this is any different from the way any other Bluetooth connected mouse would operate with Windows. For situations in which Windows isn't running and you need to use the mouse, just pull out the USB transceiver, plug that into a USB port and the mouse will function in 2.4GHz wireless mode.
If your mouse's rechargeable battery is running low, a light on top of the mouse - the same one that flashes green when you press the DPI button - will begin to flash red. At that point, you need to charge your mouse. You can do that with the included USB cable. The smaller plug goes into a port on the front of the mouse, as mentioned earlier, and the larger end plugs into your computer, a cell phone charging block, or a standard outlet equipped with USB power ports. (No charging block is provided with the mouse.) Charging via a laptop's USB port seems to be on the slow side; my guess is that the mouse charges faster if you use a 5V USB charge block instead. But you can use the mouse while it's charging, so at that point, it simply appears to the user as if it were a wired mouse, even though it's actually communicating with the computer via Bluetooth, and only getting electrical power from the USB port.
One minor quibble with the charging cord: It comes with a hook-and-loop cable tie for neat storage, but the cable tie doesn't come with anything to physically attach it to the cable while the laptop is charging. There is also no on-board storage for the cable, so both the cable and the cable tie are easily lost. It would be more convenient if the cable tie came attached to the cable, or, even better, if the mouse had a retractable, pull-out charge cable.