I also wear the feathered friends vest. Lightweight, high loft, neck zips up nice and high and is well-filled. They run a little small. I normally wear XL, and their XL fits…but with very little room to spare. I can layer it over a thicker base layer but not a decent-weight fleece. Mine was purchased on clearance, there was a fairly visible stain on the nylon on the chest.
Good observation about compressing the down. It’s important that layers over a down vest don’t really do that. It’s the reason a belay jacket, down sweater or shell you layer over a puffy need to be on the roomy side, so you get the full benefit of the loft.