The initial video demo
for Magic Leap looked very impressive, but it was just a concept video and was quite misleading. The problem is that the video shows various virtual objects that are darker than the background, e.g. The dark red robot against the cream wall at 49 seconds in.
Unlike the composited lies of the initial video, all their subsequent videos are shot through their device and it is abundantly clear that they are using an additive light technology (much like you would get from bouncing an image off a piece of glass at 45 degrees). The first thing you notice is that all of the videos shot through the device are in rather dark rooms, some very dark indeed. If you look at this shopping demo
you will see that the eyes of the weird yellow lamp creature are meant to be black, but the grey background shows through them. This is a limitation of additive light.
Now people who have used the device say they were blown away and I'm quite sure that if I saw their Star Wars demo
in a conveniently darked room, I would also be amazed. The problem is that people who have experienced the device in darkened rooms might come away with the impression that it can show dark objects, or rather, realistically lit objects, in a normal well-lit environment. In an outdoor environment, or even a well-lit room, the objects could look very washed-out, or at the very least, very bright, glowy and unnatural. If you just want to shoot glowing space aliens or read some glowy text, that isn't an issue. However, if people are expecting to see realistic naturally lit objects that actually look like they belong in your current environment, I think they may be sorely disappointed. The additive light limitations could also be a big problem for shopping applications. After all, it's a bit difficult to see how that dark green couch is going to look in your lounge if the wall behind it just shows through. Google's project tango has the advantage there since it can just composite naturally lit objects over the video feed.
I'm not saying their device couldn't be really useful, or even pretty amazing in certain situations and environments, but I think the limitations will cause issues and may put a lot of people off buying one. I could also be wrong, and for some reason they have been refusing to show their amazing light-blocking technology in their demo videos, but that seems unlikely.
P.S. Although they have been more honest in their videos recently, I should point out that their website still shows concept images that misleadingly give the impression that they are able to show objects darker than the background. I should also point out that Magic Leap have been far more honest than Microsoft who seem to exclusively composite their videos to hide their crappy field of view and similar additive light limitations.