I look at these every now and then, but haven't bought one (yet?). Part of the problem is that you need a good-sized room (or at least in one dimension) for these to be effective. And the cabling gets to be a hassle especially when an AV receiver is added to the system.
However, I know three people who swear by the old
Infocus X1. Two of them were contractors who bought the X1 to use on remote assignments (convenient, easy to carry). Unfortunately, the X1 is off the market and replaced by the X1A and X2 which use a DLP circuit. I don't know what that means except it's supposed to be good.
White walls are not good surfaces due to texturing, but they'll do. One of these guys made a cheap screen by mounting a 12-foot closet rod across the entire room, then draping some white light-blocking cloth over the pole. I think he added another pole to the bottom edge to weight it down. Lots cheaper than a screen which can go for $300 and up.
If Costco operates in your area, they have been selling a combo pack - Infocus X2 plus 7-foot screen - for about $1100.