They say the Montgomery 15 points higher, has more room, is more stable, and is faster than the P15. The P15 is lighter, easier to launch, and costs less.
I expect some people here might disagree; just curious.
(I have had a P15 for 2 years. I expected it to be slow and don't care about the small cabin; but I was hoping for better stability. It was well priced though)