Has anyone used a comp vest?

Wombat661 wrote: "I would rather have survival gear like radios tethered to the boat and the boat securely attached to me via leg leash."

That would be called a single point failure in aviation. If the tether breaks, you lost the boat and radio gear just when you need one of the two most.
If the radio is on you, then if you loose the boat you still have the radio. You loose the radio, and you still have the boat. Have safety redundancy.

If you read the two preceding sentences from my post you will see that I was referring to bulky items carried in the front packets of PFDs. From my perspective, the risk presented from a leg leash break is low. My leash is a Mocke which is quite robust, so it is unlikely to break. Secondly, I always paddle within a mile or so of land (warm water Florida), so even if it did break I am confident that I could get ashore. I am a strong swimmer with exceptional water survival skills as a result training required by my first flying career. (Applying FAA SMS risk hazard matrix to determine risk of leg leash break, Likelihood=Seldom, Severity=Minor so result is Risk=Acceptable).

There is certainly an argument to be made for adding additional safety gear to my PFD if I were paddling further from shore and/or in more remote areas. If/when I add anything it will be a PLB on a tether in my back pocket and not a radio. Based upon the half-dozen or so SAR missions that I flew while in the Navy, I have a pretty low opinion of radios for survival. They have a limited range and are hard to use when your hands get cold. Also, voice communication can be pretty intermittent when the swimmer is in any sea state. PLBs are much better in a survival position because they easy to activate and provide continuous location data.