I use the funk adpak and retro adpak all the time when practicing and playing live. Switching kits is very fast. Love the range of sounds with them. Recently bought the Metal adpak and am messing around with it to get familiar with it. Toms are deep and thunderous, kicks are suitably "clicky" and the snares add another option to the sound pallettte. I think some of the cymbals in the Metal adpak have a really different sound to the other packs. The only adpaks I don't play a lot at the moment are the jazz sticks and brush kits - but mainly because I don't play that genre too much as yet.
Well worth the purchase price, in my opinion so far.