Gap is OK, uses the standard Buhlamans ZH-16-B algorythm. It is however a bit inflexible in it's use, and I found it hard if not impossible to plan multi-level dives.
I was playing with the latest version of V-Planner last night, it seems much improved. The deco times of the VPM bubble solution seem comparable with the ZH-16-B, one of the complaints of the early versions was that it was very aggressive on it's shallow stops and people were getting bent on long deep dives. Nice and flexible to use with some simple solutions to output bail-out profiles.