I’ve got a pair of the pro bib shorts from when they were in the sale last year.
Size-wise the guide seems about right – I’m 5’8″, 30″ waist (when bloated!) and the small size fits well, maybe a little short in the shoulder straps. I’d probably go up a size if I was inbetween but maybe give them a call and ask.
Comfort is good, no problems at all and they’ve worn well, Although I use them mostly for my commute under baggies.