It was very affordable (sub $20), came in lots of colours (including this lilac colour that I love!), and is super comfortable too. The vertical mouse I used previously, a Ugreen one, had a narrower grip that was less than ideal.

The mouse is by "Sanwa Supply", model number "GMAERGWBT22V" (V for violet I presume, it shows up at just "BT22" when pairing with Bluetooth), though I'm sure there are plenty of identical models from other brands.

The plastic finish is nice and will last a long time, as there isn't rubber everywhere like on the ridiculously priced MX Masters. The buttons are silent and have a nice click, the side buttons for forwards/backwards are nicely placed, you can switch between 3 devices (two Bluetooth, one with the dongle), and the scroll wheel is nice (though not a metal one)

The mouse came with a magnetically attached wrist rest too, which is nice, and even without it, it does not suffer from the trailing pinky finger issue of other vertical mice. The magnets are strong enough where it isn't super loose but not too strong where it's hard to detach. It's a nice bonus when I'm at my desk for long hours, and it can be removed if I need to pack it.

BUT one of the main reasons I bought it, aside from the fantastic colours, is that you can use it with a AA battery! No glued in nonsense, it's super easy to swap it out, and the dongle is also stored in the battery compartment too (always a nice bonus). I use it with rechargeable IKEA Ladda batteries, and it's been awesome.