I shipped the Mentor out to the next tour participant a few days ago and have been on the road since then. Here are a few more thoughts. The Mentor Multiverse is an unequivocally great IEM. The BCD is summit-fi lending it supreme imaging capabilities-- it really feels like you're listening to a full size headphone. Sound is thick and bodied to my ears-- in terms of tuning it is excellent something of a cross of the VE8 (rich mids) and Phonix (mid-centric, amazing vocals)...then with the BCD kicking it up to the stratosphere. Sound on the whole is a nice balance of emotional and technical with perhaps a slight nod to the technical. Piano timbre and impact is a major highlight-- probably the best I've ever heard, as are female vocals. Renders any romantic mid-centric BA IEM without BCD basically irrelevant in my opinion. Bass is solid but would probably be my least favorite element of the sound. It's really good but even with the BCD factored in it doesn't quite give me the density and grip I enjoy with a planar or DD and as such this would be the main reason I'm not considering buying one-- if I spend that kind of money there definitely needs to be a DD or planar in the mix. YMMV there. Imaging and realism of scale makes it feel you're in the presence with live instruments-- this is uncanny and unique in my experience with IEMs. I don't think it competes with Traillii really-- Mentor is approximating a full size DD headphone but Traillii is closer in spirit to a planar headphone imho.
Both Mentor and Traillii impress like full size headphones. Based on my very limited experiences with full size Mentor falls closer in spirit to something like a Verite C and Traillii like a Susvara. There is a lot of audio memory hand waving here and I've never actually a/b'd the Bird and Mentor. Traillii has more of that certain "pristine" quality to the sound I associate with planars and Mentor has more of a "meat on the bone" sound in the mids that I associate with DDs. YMMV and all that.