The GK-3 is smaller and easier to use ( I was using a GK-2 origionally and kept hitting the switch on it while I was playing) and will squeeze between your treble pickup and bridge. The pickup bracket actually hangs between the bridge and the posts, so it always stays in proportion to the strings as you raise and lower the bridge. The adjustment is actually on the GK-3 pickup itself. You can adjust the curvature of the pickups ( there are actually 6 little magnet humbuckers on the GK-3, one humbucker per string) in relation to the string curvature.
There is a slight latency when triggering sounds, but that kinda goes with the territory. You play according to what you're hearing, you get used to it. Let me put it this way, it hasn't prevented me from being able to play very articulate runs,but again, as I said earlier, setting up your string sensitivity is very important. I will say that I had to set my sensitivity higher than they suggest as I'm not a heavy handed player, it allowed me to be more dynamic with my playing. On the other hand, you could set up a patch, like horns or strings, with a "heavier" sensitivity so that only when you hit the strings harder do you hear the patch. I do this quite a bit as I blend the GR-33 in with my Les Paul pickups to add sound layers.
It goes pretty deep editing wise and you can add on extra pedals, too.
Personally, I think the GR-33 is the only one to get, unless you don't want the extra flexability, which if you're at all like me, you'll appreciate.
Also, the sound set is based on the JV modules and are very usable with some tweaking. The 1st thing that I did was turn off the reverb so I could hear the patches. You have 2 sounds that you can blend for each patch and you can pick the octaves, panning, etc for each. The possibilities are pretty amazing.
I couldn't go back at this point, but that's me.
Let me know if you have anymore questions.
Lucio