I'll bet £50 the engine will sieze at one point or another.
I'm not exactly sure about the RS50, but the 125 requires a new piston at 4950miles, and a new barrel and piston at a little under 10k. (Normally if an engine siezes because of oil starvation or a piston just lets go, the barrel will often need to be replaced. This would cost around £550 to get sorted at a main dealer (not necciccerly (spelling)) an Aprilia one (I'd sugest talking to the chaps at
PJE, a place which specializes in 2T engines,) stock many parts and have very good press on the various owners forums. Considering it shares the same engine with the Derbi GPR50, having a very quick glance at a forum pertaining to those, reliabilty seems iffy.
Sounds exactly like a chainsaw
I shouldn't be one to lecture, since I myself am riding around on a desrestriced 125, but what you're doing is much basically saying f*ck you to the entire age restricted thing.
Get caught above 30mph and the police have the immediate right to take your bike there and then to a testing facility, where upon at which time if they find your bike is not restriced, they would most likely seize it, if you're lucky they would just make you restrict it and take it back for a retest in a few days time. Get caught a second time and it's bye bye baby.