Different animals.

Big difference physically. The Etys have that deep insertion that bothers some folks. The result is excellent isolation, and very little sticking out from your ear. The B2D, on the other hand, is a chonker of an IEM. I messed with multiple sets of tips until I found the right fit. YMMV but with the right tips the isolation is also solid. I could wear the Etys longer, ie a long plane ride. I've fallen asleep with both (though not recommended).

ER2XR cable isn't detachable/ replaceable, and it's very thin. No complaints about it though. Overall, it is a much smaller, lighter package. B2D stock cable is kinda meh, but there are multiple options to swap it out (including ones with microphones, or balanced 2.5mm connectors if that's your thing).

Not sure I'm qualified to accurately describe or offer much opinion about their sound comparison. Both resolve well, especially at their respective price tags. Bass is more present on the B2D, generally a fuller sound overall.

I reach for the B2D (or my Arias) more often than the Etys, but they were 3x-4x the price...

Had the same experience, bought Moondrop Arias as my first "good" IEMs in 20 years, rekindled music enjoyment for me.

Next came the Blessing2 Dusks, ER2XR, HD 6xx, Qudelix 5k, Meze 99 Noirs..... now jonesing for the Hifiman Edition XS...