They have a hole for the hook at the front but what re they like at the back?
My neoprene impact vest interferes with the back of my waist harness.
OK, it's not a PFD by definition or law, but I use an O'NEILL Gooru Impact Vest. Padded front and back, no zips or buckles. I use it with a waisty straight over the top of the vest no worries. See Sam or Chris at Wind Surf n Snow which is where I got mine (from the kiting section of the shop). Specifically purchased for wavesailing and it is comfy, doesn't rub or rash around the shoulders or arms, and is very flexible and doesnt impede movement of shoulders or torso in any way. Although not a pfd, I found that it has good float for what it is with me being 90kg. I found that the float she gives helps nicely with quick waterstarting in nasty situations when the sail is in the wrong position and requires some manoeuvring fast - which saves heaps of energy.
Specifically for flat water speed sailing I use a NP PFD, which I also use with a waisty and seat harness depending on the day. Way bulkier than the impact vest as you would expect, but floats me like the QEII. Useful pocket for spare rope and a mars bar at the front and is adjustable around the waist and side zipper. Hole for harness hook at the front. The bulk is noticable when wearing, esp compared to the impact vest, but it is a proper PFD, and if I were to be knocked unconscious, I would prefer to be wearing this baby.
I use the NP vest and waist harness. Sometimes withe a wetsuit or rashie. With everything on you get a a bit bulky. Waist harnesses tend to ride up on your abdomen so they need to be tight. Body shape regulates how much it moves. The NP vest is designed to fit around the waist harness and uses a loop to go under the harness hook. Overall it is a good design but does need plenty of adjustments in your session. Despite this I always wear this combination as the vest makes water starts less effort and provides good impact protection if things go pear shaped.