I like them all if they say ys . There is only one kind of good model engine the one that runs. I LOVE ENGINES WITH PROBLEMS . It dont matter if there four strokes or two and gas .I like buying them when no one know how to run them. A os four stroke is good choice and yes you need a tach for tuning. I WORST THING TO DO IS FLOAT A VAVLE DUE TO IMPROPER TUNING! And to small of a prop! a os 120 will swing a 15-8 ,15-10 ,16-8. They are a fine running engine.