My perspective: I'm a working sea kayak guide in Atlantic Canada, in an area with a heck of a lot of granite and intertidal slippery sea weed areas. I take the choice of my footwear very seriously. My footwear not only keeps me safe, but my guests as well. Confidence in my grip is essential to me doing my job.
So with that, I give these paddling shoes a 9. They are better than most that I have tried, but still do not give me the same 100% confidence that I have with my very old, very glued back together Nike ACG Mid Tokatees (unfortunately, not made anymore!).
That said, the Son-R Buckle is a solid piece of footwear. Well made from what I can tell after initial test run. What I really like is there versatility. This could be one pair of footwear for a summer sea kayak trip. Both good in the boat, then for an adventurous island hike, as they have good support and feel on land and in water. Probably fit about a 1/2 size too big if you are just bare footing in them, but about right if wearing over a bootie or drysuit. The buckle seems solid to me, and think they would not come off at all in whitewater river swim (haven't tried yet though).
I look forward to getting good use out of these, as they are great in the summer, allowing my feet to breathe a little more too. Certainly better grip than any sandal that I have tried around the water, and they fit very well in my kayaks too (touring or ww). My one caveat is on the grip. While quite solid in comparison to many others on the market, I'm still unfulfilled in my ongoing quest to hopefully one day retire my old Tokatee's. (or until Aquaseal can't keep them together any longer....)