Well, I got this on Monday (it arrived incredibly quickly).
Surprisingly, they somehow found a way to make it louder than the full-sized rumble pack. The rumble seems a little less "rumbly" and a little more "clicky" than before as well.
All in all - it's ok, and it's nice to have something other than a spacer in my GBA slot. It does add somewhat to the Starfox experience, and I'm hoping it'll do the same for EBA. Hopefully more games will come that use it - I've always felt that the DS should have had rumble (and tilt for that matter) built into it from the get go.