I don't get the Off-TV praise. I've spent my whole gaming life trying to find ways to play my handhelds on a TV and you guys are doing the exact opposite. The whole thing sounds like a handheld without any portability which seems like the worst of both worlds to me. Having a tiny screen and speakers is something you tolerate so you can take your games with you when you leave the house.
I have a wife and two kids who share the same TV where our Wii U is hooked up.
Yes, if given the choice I prefer to play on the big screen. But off-screen play allows me to enjoy games while sharing the TV, which can be nice when kids are around or allows my wife and I to hang out together on the couch while watching different things. The best part is that I can (often) seamlessly switch between big and small screens depending on what's happening, getting the best of both worlds when the opportunity presents itself.
Not a necessary features by any means, but it is convenient and has seen considerable use at our household... If there weren't four people vying for screen time then it wouldn't really matter I guess.