They both allow you to do things over 3G that you aren't suppose to do unless you're on a wifi network like use face time and get apps larger than 20MB. Basically like I said anything that could only be done on wifi it enables over 3G. I use 3G Unrestricter. Never had a problem with it so I never tried the other.
I used Facetime with My3G the other day with my wife. I had no issues and it didn't seem to lag at all. My wife was at home on our WiFi network and I was at work on 3G. We talked for around 5 minutes without issue.
On iOS 4.1 3G Unrestrictor has major issues for me. When me and a friend attempted to use it I would call him and hit FaceTime. He had to also hit the FaceTime button as he got no alert he was getting a FaceTime call from me. If either one of us tried to just straight up FaceTime with no call it just showed up on the other persons phone as a missed call with no ringing or anything. Very annoying!!!
On iOS 4.1 3G Unrestrictor has major issues for me. When me and a friend attempted to use it I would call him and hit FaceTime. He had to also hit the FaceTime button as he got no alert he was getting a FaceTime call from me. If either one of us tried to just straight up FaceTime with no call it just showed up on the other persons phone as a missed call with no ringing or anything. Very annoying!!!
Are you on limera1n or GP? Do you have the newest version of 3GuN? It works fine for me...