ye you can fit them on mfi, they cut the coil. A soft limit feels like a missfire and the engine goes a bit feathery, designed to limit nicely when accelerating normally upto the limiter in gear, a hard rev limit sounds more like a stardard bongbongbong limit, this is more for a very fast rev up ie when a gear is missed or wheels spin, this hard limits to reduce the maximum engine speed which could occur when a wheel with momentum spins for example, or the engine is revved hard out of gear, the momentum of the wheel or flywheel can actually throw the rpm past a rev limit, thefore a soft limit leading into a hard limit is used to minimise this and reduce shock loadings that would otherwise be caused by a nasty limiter on its own.

does that make sense? got a cracking head ache lol