well i received the twf21. I'm not really a huge fan to be honest. They sound remarkably flat. The out of head soundstage takes a second to get used to coming straight from a normal dynamic iem. It fits good. There just isn't enough energy in the sound for me, both my main phones, the mspro and brainwavs m2 have a very forward midrange, which gives more energy.
The twf21 really does sound extraordinarily flat to me. The twf is strange in that it has alot of subbass, to me it drowns out the midbass. it results in not enough slam impact from the bass and more droning boom boom sounds. The mids are affected by the huge subbass too. not in terms of bass bleed, but purely the subbass is so loud it becomes harder to hear the mids and their detail. I can see why some people love this, it does have bass unlike any other phone, as in not many phones have that amount of subbass to midbass ratio, but hey i call it unnatural.
I've only had them a day, so i'm hoping my opinion changes as i listen more, otherwise i'll have to sell them.