Hi, I'm the one that wrote this app, so a few replies:
The app is for controlling a computer during presentations, if you want to use it from the couch, or any time you don't want to be tied to a larger keyboard and mouse.
I actually wasn't aware of Gmote when I did this. I've checked it out, and it's nice, but it's primarily a media control app. The keyboard lacks control keys, and the shift key seems to work inconsistently. I wanted to make a more narrowly-focused app that does one thing well. Other features that Gmote lacks are things like a scroll wheel, which I plan on adding soon.
The black keys are just a protective rubber cover that I got from my local Mac store. $10 bucks or so.