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.
I understand. What about semi-vertical models?
The semi-vertical ones help compared to a standard (horizontal) mouse, but as someone who had a lot of pain, they were not enough for me. For example, I had the Microsoft sculpt mouse, which came with their split keyboard (the main reason I bought it) and still experienced pain. Then I went more vertical to the Logitech Lift which was better, but did not eliminate the pain entirely. Finally, I now use the Evoluent Vertical mouse and now no longer experience pain in my mousing hand.
The only drawback is when I used a standard mouse (totally horizontal), I used to switch hands and use it ambidextrously. Now I obviously can't switch hands with these mice.
I think for someone who doesn't experience persistent pain, a semi-vertical mouse may be well enough.