having gone the megasquirt route on my various builds of engine over the years it's great in many respects, very versatile unit.
however and it's a biggy, it takes time, fuel, more time, more fuel and patience to get your mapping skills good enough to get it nice to drive.
pay a mapper and let their years of experience save you a fortune in time and fuel.
if you really want to learn go for it, i haven't had a failure of ecu at all, just wanted to learn and thought i'd save loads, handy as i've changed spec loads of times now.