Actually, it can be used close up. I've done it before. As I mentioned in an earlier post (I think), I performed it in a waiting room for a couple kids. There was no dimmed lighting, no "stay ten feet from me" or whatever; I just did some simple moves and kept them entertained.
More recently, I performed a couple short D'Lite sequences for two of my coworkers. For one of them, the lighting was somewhat dim, but still very easy to see everything, and for the other, the lighting was perfectly normal. Both people couldn't see the gimmick, even though I was 3-5 feet from them.
If you handle it right, it's perfectly fine for close up work. If you're awkward with the handling, then, yeah, you should only do it on stage, when they can't get close enough to see the gimmick.
Oh, and D'Lites come in packages of one, not two.
From the FAQ on the D'Lite product description here:
"Q: How many D'Lites come in one box?
A: One D'Lite device is included in each box."
If you get the D'Lite Combo, you get two devices. I'd just get two individual D'Lites, though; in my opinion, you don't need the video to learn how to use them, and it's cheaper buying two singles than the Combo.