Speaking of lemons, no-one have had as many as OS anyway. They are the only engine manufacturer who have had problems with nickel peeling in their sleeves (La series peeled, FX series peeled, and even ax series peel, although less frekvent)
The ulitimate 70 fs was a total fiasko and was discontinued after a short while, the first production of the 91 FX had lots of problems so they had to change the remote needle assembly on the next generation. OS is surely no guarantee of success, only the fanatics think so

They do make quite a few very good ones also

I have had a TH 75 which ran very strong, I have also had great success with Magnum, ASP, MVVS, OS, YS....etc

Most engines out there nowadays are good if one know how to handle them and solve minor faults like small airleaks, which can occure with both cheap and expensive engines.