They are ok machines as long as you get them for the right price. Basically your getting a Sherline milling machine that has been converted to CNC. The trouble with these machines is the hardware will only work with the original D&M software which is totally out dated and will only work with a computer running a DOS operating system. To get these machines up and running with some thing like Mach 3 software you need to do a retrofit and replace most of the electronics.
You can re use the spindle drive, power supply and some other bits, but you will need to get a breakout board, stepper drives and motors. If you want to save some cash you can re use the original stepper drives and motors, but I found that they are really weak and easy to loose steps when milling. It's a small machine so you don't have to get super large stepper motors and drives, just something a bit larger than what it has.
If you get them post some pictures. Make sure to include some pictures of the electronics so I can see which model you got and I will see if I can help you out as I have converted a lot of these machines.
Dale P.