It was very affordable (sub $20), came in lots of colours (including this lilac colourway 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 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, and you can switch between 3 devices (two Bluetooth, one with the dongle)
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.
It's no "gaming mouse", but I use it to play Minecraft, and it works well for that.
I'm curious, if you like vertical mice so much why not try out a trackball? They're not for everyone and they do introduce a learning curve but I made the switch long ago to curve any possible RSI I could be setting myself up for in the future and cannot go back. It's infinitely more comfortable than optical. It does introduce some challenges which in my opinion are worth it, i.e "sticktion".