OEM mounts are very expensive but very good. They are eingineered to be soft and let the engine
bounce around a lot in seas and are good at absorbing engine
recommends replacement every two years, but that is mostly BS IMHO. If the rubber is good, isn't bulging out of the sides and there is 3/4" or so of clearance between the metal pieces, they are probably ok.
But engine vibration is almost certainly prop/shaft vibration. Make sure that your prop, shaft and coupling are true and your engine is aligned before even thinking about engine mounts to solve a vibration problem.