I beleve a good trainer is something that will allow all abilities to fly . The enstom is probably the easiest one to fly , with superb stability . I would reckon you would have a good chance getting it on the deck in one peice even if the cyclic came off in your hands .....excellent safety record . The 300 is a "proper " helicopter and feels like one . I felt very safe instructing and being instructed in one , so a great trainer . I am sorry but the R22 just had me sitting on the edge of my seat and i did not feel safe . I believe it may be safe in experienced hands but again some of the most experienced pilots have come a cropper for no good reason ...just flying along ...a very experienced friend flew one ( without the robbo "extra" training admittedly ) and in moderate turbulence it just decided to roll almost inverted
He has many thousands of hrs but will never do another in a 22 .
I would pay a bit more and learn on a proper chopper .