I've looked at the Wavedrum Mini too as its more mobile (battery operated and speaker), but it seems like an expensive toy to me. The main thing that puts me off is that velocity is used to trigger different sounds in a kit rather than to increase the velocity of the hit. Seems odd to me (unless the kit contained the same sound at several velocities but I don't think that's the case). If anyone has this and is enjoying it then I'd be interested to know what you think.
I've been using Impaktor on the iPad and I love it, hence looking at the Wavedrum. The thing with Impaktor is that you can't use it live whatsoever as it uses the microphone input to trigger sounds (so the ambient sound in a room/club/pub will also trigger the sound). Great for studio use though.
Cheers
Alex