Stablity wasn't my concern but getting swamped. If a wave or wake was to hit the side of that yak or a canoe it could fill it up pretty quickly I suspect. A SINK offers some protection, an SOT its not even an issue. Its probably not a huge issue, just the first thing that came into my mind when I saw the design.
The Native Magic seems to have many of the same advantages but as an SOT.
I can stand and cast out of both of my SOT's a FishnDive and a Marquesa - I'm a good sized guy and not all that coordinated. I think standing and fishing is highly overrated because if you catch anything decent you have to get down to land the fish. The Marquesa is nice because it is perfect for kneeling which makes it ideal for spotting a fish, praying, casting, and hopefully landing fish.
I always find it interesting to see what guys like and dislike in yaks. Like some people don't like sot's because you get wet, I like them for exactly the same reason, catching the occasional wave on the chin is part of the fun.