I use my Tom Bihn Aeronaut... It is black and wheel-less so it
already looks small even though I can pack a lot of items inside.

The GA's never bother me about stowing it underneath on the
small jets. I never fly anywhere on the prop planes so I have
no experience to report with them.

I only take 1 bag... and that 1 bag also has my CPAP so there
would be some discussion if they requested to tag it.