[RidgeRunner]

I had a 2001 -225 Opti and currently run a 2003 -250 Opti. Neither have high hours,(600 to 700) the 225 was near trouble free, a harness replacement under warranty, a poppet valve after warranty and plugs for good measure at 500 hours. Always ran ring free and tried to keep non-ethanol in the tank.
The 250 is new to me, but the history has it as trouble free thru the warranty and a denied claim for a compressor replacement sometime shortly after the warranty ran out. As an XS motor it requires 91 octane or better, I mostly run 93 octane with 10% ethanol.
The compressor seems to be the weak link IMO but I have no personal experience there. I have heard of some coil issues from other owners.
X2 what Ferm said, The later ones are better. With the early ones you either got a good one or you didn't. Early on Merc was replacing lots of powerheads with less than 50 hours, if the Merc owners knew then what they know now, there would have been some litigation over the frequency of the compressor failures. Merc claims the Compressor has been redesigned.
The go-fasts are starting to warm up to the Direct Injected Mercs. Dave Bush has a Level 1 kit that hops up the 300xs Mercs. They are making reliable power at 15 to 20% over stated hp. The internals seem to be stout and they have thousands of hours of testing time running them hard on the dyno. The tuners seem impressed with what Merc engineers have come up with. (meaning they had to do some serious homework and testing to better what the factory came up with.)
I wouldn't shy away from one so long as it checks out. They are heavier than advertised by a touch. It would be hp a plenty for a V20 they are snappy and fuel efficient. Talk the dealer into 30 days from initial water test on the warranty. That would be the only fair way to ensure you got what you paid for.