If you're trying to build something quickly, it's not a bad idea to use an existing style and layout to just get it done. Thinking about design too early can be an unneeded burden. I wouldn't propose they go live with it, but it's fine for early development.
Yes, I like it and it works well.
I respect that it works well, but there's a difference between using a style as inspiration, and outright ripping it off. This strikes me more as the later.
(I think Google won't mind.) It doesn't really show in the screenshots but it does feel a little different from the Gmail/Google style when you actually use it. But your comment is fair enough, it is quite close.
perhaps its integrated into gmail? that would be pretty neat, I'm hoping it's a google marketplace app.