There are a few things about the kit I'd question. I don't know anything about them but the few things are. Steppers being small as they are & direct drive to boot I'd be worried about having enough power & resolution for a larger size table. I really don't understand using a standard variable speed DC motor on the Z axis & manual jog. I'd want my Z axis to be under CNC control also. If you are planning on using plasma & especially cutting thinner material you will also need a THC (digital preferred) to keep plasma cut height correct as your sheet of stock comes & goes with heat.
Maybe I didn't read far enough or understand all I did read. I think you can do better as far as price to build your own.
Their package is attractive for only one reason I can see. The rails & rack gears etc. come already assembled. However you'll still have to mount the "T" rails accurately along what ever table you build.
In a nut shell. I wouldn't buy it.