I have run nothing but 10W-30 in my old 98 300 TRX, most of it regular old yellow bottle Pennzoil. However, that machine didn't call for anything other than an automotive rated oil, and many/most people never had issues with standard automotive oils in those engines. The newer engines seem to be pickier and do call specifically for the JASO - MA rating. Ordinary 10W-30 will undoubtedly still work most of the time, but the right rated oil is the only thing I would run in one of the newer Hondas. It costs a lot of money to get oils tested so they don't all get tested for every rating even if they might qualify. However, I suspect they would invest the money if they actually formulated the oil to meet a certain test. Consequently I would probably not run an oil that didn't specify compliance.
BTW, I am not brand loyal to machine manufacturer oils at all.
