I don't like them at all.
They'd be extremely awkward without any support if you're playing anything that depends on speed. How are you going to support the device when you have to quickly move your thumb back and forth from the stick to the buttons? It's the return of the Claw. The guy in the airplane picture looks like he's in hell. In the real world, he'd switch back to Vita-mode in about 5 more minutes.
The picture below it, with the people gathered around a small screen at a party playing on tiny controllers ... yeah. That would be lucky to last 10 minutes. Which, actually, makes me wonder if you can dock your Switch into someone else's station, if you know what I mean.
The best thing about this gimmick is that you don't have to use it (I assume). The worst thing is that it adds cost and increases the chances of loss or product failure. If I bought one, I can't imagine using them like that except once on a blue moon.
