I'm not sure, but it looks like the release is that red pin thing. It looks like they've designed it so that it can't be bumped under most circumstances.
Looks like great system, and not as awkward as the one Rrdstarr proposes. But I'd tend to agree that it may not be suitable for an SLR on a kayak, but can't you mount the waterproof ones to tripods etc? If so, then it'll mount to this.