agreed. for someone who happens to have multiple detachable IEMs already, the BT20S is the way to go (as long as the combo don't produce too much hiss). even if there is an increase SQ on the ES100 amp compared to the BT20S, it will only noticeable on a direct side by side comparison. that difference would easily forgotten because of the increased mobility and convenience.
for information, from my collection only the DM6 that produce quite a bit of noise, the B5+ has really low noise, and the others (earbuds included) have no noticable noise.
@HiFlight has already nicely answered the question
I'm using whirlwind tips, and because it's almost flush with the nozzle's edge, the insertion is quite shallow. just think of it like the X12 deep, but the pointy part is more snug because of the silicone. so isolation is just slightly above the X12, but still lets in conversation in.