I have a number of YS engines, including a few .63s. While they are awsome running engines, they are indeed built for performance. I have run them on 15% nitro, but they don't perform like they are meant too with the lower nitro. 20% and above is better to get their expected performance. I do not consider them in this 50 size class. More likely in a 90 size. For first time users, they are a bit more advance in tuning and plumbing, but not enormously difficult, just different than other 4 strokes. That is why I would think an aspirated engine would be a better beginning engine. Isn't Hobby people running a sale on Magnums right now?