I’ve never heard those particular ear buds, and I’m not really sure what your bass preferences are either! From skimming a couple of reviews of the JBLs, it sounds like they have quite a bit of punch in the bass. The M20X’s will have much less, most likely.
So if you want less bass and you’re not paying too much for the M20's…then the only way you can find out is to try them!
It’d be hard for me to be more specific without having heard those ear buds or knowing more about your personal preferences. You could also try posting over at the reddit headphone advice board to see if anyone could help you there.