Have you read the thread at http://www.cnczone.com/forums/genera...y_chinese.html? Those kits can work, especially on a starter or low-end machine, and many people who are looking to get a low-cost start go with them, but many other people report problems as well, so they eventually end up replacing the driver with something better (such as a gecko G540), while retaining the motors and maybe retaining the power supply, but then the hoped-for savings do not materialize. A G540 (which will support 4 axes) costs about $250 all by itself, so it's not surprising that when compared with a $250 package that includes a driver and motors and power supply, the Chinese package looks attractive at first.
If you have some experience with electronics and soldering, then there are some modifications that you could make to the driver board to improve its performance and operation. Also note that sometimes the motors sold in those kits are not well matched to the drivers, and/or the drivers can not support a high-enough power supply voltage, leading to disappointing performance. Support from the vendor is often unavailable, which may be an important consideration.
Also note that the Mach3 disk that they usually send out with those kits does not give you an actual Mach3 license, rather you get a version of Mach3 that you could just as easily download for free, which will run G-code programs with up to 500 lines of code, but if you want to machine anything requiring more code than that you will have to buy a license for the software.