Best In-ear monitors under $350?

Oh yes! Let's just dismiss a potential great bargain because it was done by a professional reviewer who relies on measurements as well as listening (headphone and EIM especially). All I'm saying is go READ the review, then make up your mind after you have more info, not before. 

Yes, definitely go by measurements.  Can’t possibly go wrong there. At 50 bucks they must be the best bargain in all of audio.  Ehem.  I’ll recommend the Timeless 7Hertz as a great all-around IEM. 

ASR just measured a $50 IEM that he says are fantastic. Check them out, if you can get a pair.

Cardas A8 are excellent - very smooth and easy to listen to.

I am using 7HZ x Crinacle Salnotes Dioko, just for 220 dollars. 

Still, it has a cleaner midrange and a slightly smoother lower treble (in my opinion). Despite the fact that the latter is superior in both categories, the former has great detail and resolution for the price point.

Pros:

tonal harmony

no fatigue

Better setting for direct competition

Good technical value for the price range

Cons:

Bass shy

Treble is still a bit awkward but better than the direct competition.

The fit as it seems is less complicated than the other planers I’ve tried.