I just rebuilt my Dad's MS250C with the easy start. I have an easy start on one of my saws too, although I don't need it, but the Stihl one is better made. It's kind of funny that it's a metal casting on an otherwise plastic cased saw. This makes sense though because the large spring in these systems has a lot of force, and metal is a better material for a housing containing a big spring like that. Anyway, it works OK, and was a real benefit to my Dad when his shoulder was giving him trouble a couple of years ago.
One caution though - my easy start saw is modified and has more compression. The starter spring is barely able to overcome the increased compression at times. The starter on my Dad's Stihl felt about the same on that stock saw - there were times when it didn't pull over immediately.