If they were the replacement for the C420, once boats start aging out of sailing programs and the wealthier sailors age out there would be a swamp of low priced boats of every condition. From cut up and throw away to yard princesses that sat with the cover rotting off them.The M15 looks like a great boat, but it's pretty low-tech. At 230 lbs with aluminum spars and white dacron sails, it's not exactly cutting edge. I don't see this as a youth boat so much as a fantastic 2 person boat for couples, or parent/offspring (remember when that was "what you did"?). I do not believe having M15's replace 420's will do anything for post-school sailing. When I got out of school, I was in no position to buy a boat of this calibre - a used Laser was the best I could do. Plus, for most the focus is on careers and relationships. I think most clubs have strong youth programs, then a gap, then parents returning to sailing with their kids in the the youth program.
I think many people lack the wonderful experience of sailing a C420. You really should rig one up and go for a spin in light air and medium air. You'll never forget it.