It's convenient because of the small size.

I once got an bigger "upgrade" for my small wacom tablet, but it only collected dust. It used too much space on the desk to always keep it ready, and the larger active area meant too much travel distance when using the pen as a mouse.

And concerning Wacom, they were the first to have someone working on Linux drivers, and the only one for a long time, back when tablets were new. Not sure how it is today.