Since there is some discussion / recommendation of the TRN BT20:
I've got me two pairs of them (one 0.75 and one MMCX) and the first IEM I've tried was the TRN V80. I was shocked about the bad sound quality (static / background noise, hissing).
I thought I've got a defective BT20 at first, but then I've tried other IEM's (TRN V20, BQEYZ BQ3) and they work perfectly.
So it is very strange that just the V80, which is used for the product photos of the BT20, does not work for me.
The MMCX type I have currently paired with the Nicehck P3 (11.11 fukubukuro).
My experience with TWS IEMs so far is that it does not just depend on sound and runtime.
With my first pair (QCY Q29), the seat in the box and thus the connection to the charging contacts was very unstable.
In addition, they have turned on by themselves and the power bank function of the box has quickly failed.
The next pair (Chinese Noname) discharge themselves and the box very quickly by itself, you have to constantly recharge without having used them.
My last purchase, "Anker Soundcore Liberty Air" is much better, but also much more expensive.
Out of curiosity, I recently ordered an "X6 Aurora Wireless Bluetooth 5.0 Headset" from AliExpress. It has 2 dynamic drivers per side and the design is similar to the BT20, which should give a good runtime. In addition, I found the colour really cool...
So far my two cents to TWS, there is indeed a separate thread to it.