I have looked at just about every laser and optical scanning system out there over the past ten years or so, including some at US$100k+. To a large extent you get what you pay for but often the software is as much of the solution as the hardware.
If you use a laser generator and its line is too thick you will get poor results. If you scan erratically; the same result. The better the fine laser line the better the software can do its thing. The optical scanners are good too but the models you often see in Gallery pics are so often shown with texture maps fitted to the data. This makes the model look great but may not have adequate surface quality for
CAD or downstream
CAM.
Optical systems have calibration setups that can be tedious and multiple photo-masking work to follow the (quite rapid) scanning routines. Laser scans will usually require multiple scans at different angular positions and a subsequent "stitching" or merging of them into one 3D model. This can be a very difficult and lengthy procedure unless you have one of the expensive programs such as Geomagic or Rapidform. These are just 2 of the several programs that can merge scans very easily and very accurately but they cost thousands of dollars to get a license.
The David system is excellent and will require that you can move the laser steadily and smoothly to "wash" the model with the laser line if you want good results. Intricad offer the Triangles kit which is very well developed and presented and simple to construct with basic home workshop tools.
Of all the web-based suppliers I've dealt with over the past ten years though, I'd have to say that Dan who sells the kits has the crown when it comes to response-brevity. Maybe he hates using a keyboard. Anyway, he isn't big on chat but he does have a very nice kit at a very good price and it arrives (as mine did) very promptly. I've just built it so I will have some more info on how good the data is when I try it out with both a Logitech 9000 WebCam and a Sony HDR - SR12E digital video camera. Thats about as extreme a camera comparison you could ask for.
By the way, I also bought the NextEngine laser scanner when it first came onto the market but my experience with it was not what I would have expected.