There are a few that are very thin like that. We used one under our cabinet as you're discussing and we also used one in the side panel(s) of a fridge and cabinet to allow for a hidden plug when we had no uppers to hide it under.

You can see where the plug is when you get very close, but not from any distance away:

We used those under all our cabinets instead of plugmold. Our electrician said he couldn't find plugmold in any color except black & tan and our cabs are white, so those 2 were no-go colors + we had an issue with disguising the wiring that went into the end of the plugmold from the wall. The slim outlet boxes are a wonderful alternative.

Great idea!

There are two box sizes. The larger size holds a GFCI receptacle. Any receptacles in the circuit after the GFCI receptacle can be non-GFCI and will still be protected. I think I'll put switches near the sink in one of the smaller boxes to control under cabinet lights and the disposer.