I’d advise caution and would recommend approaching this purchase carefully. The two options you propose here are significantly different in terms of expense and, by extension, risk (if you buy new). The Odin are, what, $3,400 whereas the MEST are $1,400? I’m also not sure how similar they are to one another (based on the impressions and reviews I’ve read).
I realize you can’t demo these IEMs but it doesn’t seem as though you have pinned down what it really is you’re looking for. I fear you might be disappointed with either of them. What of others like the Campfire Solaris or the Legend X (I mention the latter since you seem to like strong bass emphasis)? Or do you want something that sounds different to the Atlas and that would complement it?
It might be worth checking out these threads:
and
I’m sorry if this comes across as preachy - if you’re fine with the risk, or if you’re buying used, then have at it! It’d be great to read your impressions!