I've had this vest for about a year now. I paddle primarily open boat in both lake and whitewater. I have used it in a touring kayak and WW kayak several times. I like the fit and really appreciate the cow-tail holder, and the QR harness. Belay loop is a bonus.
Great mobility and comfort. Pull-over design is very secure and allows for the large main pocket and doesn't require re-threading the rescue harness every time you don the vest. Downside is it can be a pain to pull a vest over your head to put it on - tho' it hasn't bothered me much yet.
Main pocket could use a small inner pocket for key/lipbalm/etc. Handwarmer pocket comfy but unused by me - it's always been warmer to tuck my hands under the vest next to my body - wish that the handwarmer pocket had side closures.
Good side impact protection built in, spinal protection good where the vest covers but it doesn't cover very high up the spine - a protection trade-off to mobility.
The Aquavest 300 IS expensive but probably one of the three best WW rescue vests out there. Stohlquist X-Tract-D (problems with pocket durability and abrasion)and the Kokotat Ronin Pro may be two other contenders