It sure has been a week for twin-thumbstick portable gaming. In addition to the PlayStation Vita (which has two thumbsticks built in), I've been playing around the the "Circle Pad Pro" attachment for the Nintendo 3DS.
The Circle Pad Pro is a chunky plastic contraption that fits around the 3DS, retrofitting it with a right circle-pad (basically, a right thumbstick), as well as a second set of shoulder buttons on the back. I haven't been using it for too long, but I gotta say, despite some annoyances, I like it!
It is still clearly a retrofit -- it blocks access to some of the 3DS' vitals, so you'll have to put it on for some games and take it off for others. That's annoying. But all the same, it's already significantly improved my experience with Resident Evil Revelations, to the point that I would no longer want to play the game without it.
Check out the video above, in which I demonstrate how the Circle Pad Pro works.