The stretch vest is sized a bit small (I normally wear large but got the size XL) and it fits perfectly. Had minimal flapping when I get up to speed specially on the downhills and the weather is somewhere in the 50s or low 60s.
I bought this for my partner for Christmas. He usually wears a medium and occasionally a large. I ordered the large and it is definitely a race fit. It is very visible and folds up small to put in the pocket. Looks sharp but order a size up.
Used this for a ride between 32-40 deg f. I would have been miserable with out it. I do have a single issue with this, but more so because I am an odd shaped person, I have a very long torso and it isn't exactly long enough to stay down in the front. Normal people shouldn't have an issue with this