I don't use a tablet regularly as a mouse replacement, but from my experience of using it for image manipulation:

1) Small sizes scale up surprisingly well, but one model bigger might be preferable.

2) One should test the feel of the pad -> there are different surface types (some are very glas-like, others offer more resistance), and different styles of pens, which all feel different.

3) I feel like many of the pens are quite uncomfortable to hold. If I had to use them for longer I'd probably look into finding 3rd party alternatives or a small pen I can embed into a custom grip. Different styles to exchange regularly (every 30 min or so) would also be nice.