I had an Irving .40 - after 8 hours the rod had to be replaced. After that it ran for around 2000 flights before it just wore out from use. My OS .46AX, after one solid season of flying, is still running the original glow plug. Hasn't missed a beat. Just out of personal preference I've flown mainly OS, but also have TT and ST. But like any engine, beyond initial manufacturer quality, the operator can kill it just as fast than anything. Properly operated and maintained, any good engine should, be it OS, TT, ST, Magnum, Jett, etc. should last several years.