Raw bass power is exquisite with great rumble. Sub bass impact is mind blowing, violent, like never I've heard that... and I'm a basshead.
Mid-bass are present but not so much, low impact is really really low and not based on low-mids/mid-bass. I'm glad voices are put upfront of the stage, that's not a V shaped tuning.
Trebles have lot of extension without any aggressivity or spikes and remind me VE8's presentation.
That's though quite difficult to describe the sound of an IEM after having it discovered half a day sooner...
Not to worry, I know its early days for you.
I know Fred wanted to give the Mentawai more subbass than the Traillii and it seems the balance has shifted down further to sub rather than midbass and that should make for a nice open midrange. I just hope its retains some warmth and organic character. I've heard from others that it manages 'organic' better than Traillii, so I'm not too worried in that respect.