The design reminds me of the iControlPad, only a bit sleeker. But that had slide pads.
I suppose this would be nice for side scrolling games, but it looks pretty useless for any game with analog movement. But at that point, you may as well use a NSO SNES controller, or a SN30 (Pro), as the addition of extra buttons and a second D-pad won't be useful in 2D games anyway.
I guess maybe for some games (stuff like Tetris 99) the arrow buttons might be slightly superior to a D-pad, to avoid accidental inputs, but you would be fine with just a D-pad as well. And the second D-pad just makes no sense, when the right analog is usually used for camera control or free aiming, which is awful with only 8 directions of movement.
Which makes me wonder what game(s) they had in mind when coming up with this design, and what the thought process behind it was. Are there any games that for example use free aiming but only in 8 directions?
It also doesn't look terribly comfortable to use. Looks like your hands would cramp up after using it for a while. Which is the same problem I get with pretty much any handheld console, but if I'm bringing an extra controller with me I would rather bring something that's actually comfortable to hold.
I see one potential use for this where the layout actually makes sense and that is N64 emulation for games that make use of the D-pad (on a phone, tablet or the Switch itself)
As the N64 controller has a pretty unusual layout plus more face buttons than what controllers normally have, and since this has an extra set of buttons, you can map one set to the C-buttons, and the other set to A and B and maybe quick save/quick load, speed up, or whatever else you feel like. But the layout would still be reversed (C-buttons on left side instead of right side) which may not be great for some games. And again the lack of any analog sticks means its usefulness is limited. It would work great for Mischief Makers though, as the C-buttons are used for jetpack movement, and the D-pad is used for normal movement, it makes more sense to have both on the left side, leaving your right hand free to use the A and B buttons.