I have the old version of the hanger nine p51 that has been rebuilt several times and I have used the real cheap HK retracts that operated for twenty wobbly flights, I now have traded them in for the metal trunion version of the same retract. They while not perfect are better than before but HK is a crap shoot, Bought four of them and three of them worked. Support is non existent from HK. The 5mm studs I have attached to robostruts is soft but usable so far. Definately don't trust in a giant scale master piece,but in a 20 year old arf I'll take my chances. Take risks on the plane but never on the safety of others or yourself.