I'm relatively new to cold-weather riding -- for the last 6 years, when the weather got cold, I'd give up my ride for the warmth (?) of my gym's outdoor pool and the companionship of my fellow whacky masters swimmers. But the pool is not something I'm comfortable with in COVID times, so I had to find another way to spend more of my exercise budget outside on my bike.
I purchased both the Zero Bibs this year, and have no regrets. I've found them to be exactly the right weight when the temps are between 20 and 35. The compression is great, too, and I think that helps with keeping my muscles from seizing up. Any colder, and you'll find me on my trainer, but I am so thankful that these bibs have given me an extra couple dozen days every winter that I can be outside.
One note: the Fly Free feature hasn't been used outside yet....I simply can't bear exposing my behind to those kinds of temps, but I can attest that this feature makes that last minute pit stop on your way out the door that much less annoying!
I'm on the cusp of small/medium in this particular style. Medium might go on a bit easier, and be a bit less tight in the shoulder straps, but the garment has loosened up a little with a few wears, so small was the right choice.