skyhawk stage iii

I'm going to be ordering a 4 stroke engine kit off of Bicycle Engines, Motorized Bicycles, Bicycle Motors, Motored Bikes: 2-Stroke & 4-Stroke Kits! and I want input on both 4 stroke engine kits. What one lasts longer? Less problems? Etc 4G T Belt Drive 4 Stroke Engine Kit 49cc 4G T Belt...