I have the Ultragaff, but I never use it. To me just the fact that the spectators know that there needs to be special cards used. This doesn't apply for some tricks such as double backers and such, but for tricks where you move the queens to one card and etc, everyone knows that special cards are needed due to the fact that a spectator knows you can't move ink. Now I know the whole purpose of magic is doing something impossible, but gaff cards usually just seem impractical to me, but that's just my opinion.
Gaff cards to me are like linking rings. Everyone knows that matter can't pass through matter (solid matter anyway), so the only possible way it can be done is slits in the rings. Now I've seen people that can do this trick that stumps me, but the fact that there has to be a slit in the ring ruins it for me. It is still a great trick, but it seems like the first thing that pops into spectators miss is that the rings have a slit in them.
This is just all my opinion, and I am just letting you know what I think of them. If you can pull it off, and they work for you, by all means do it, but I just don't think they're right for me.