I've found them to be fine on Linux. It does the same 'switching' thing that it does on Windows so that when you're using the microphone you get worse audio.

I run Fedora, so maybe I've been picking up new versions of things like PulseAudio.

This is probably what you want (your QCs support it): https://patchwork.freedesktop.org/patch/245272/

AFAIK I'm not sure you can make HFP sound better. Now some A2DP codecs do support a sorta backchannel to also allow mic unfortunately the support is not currently there yet in linux.