Sainsmart has an incredible customer service. I have a 4030V2 cnc from them for almost 8 months and am very happy with it.
Last week i suddenly could not connect to the control box anymore.
After having contacted Sainsmart they asked me to do a few tests and when those did not improve things they concluded that the control box must be faulty and within 3 days of the first contact they decided to send me a new control box under warranty.
I call this amazing service and a very possitive experience.
I do not hesitate to recommend Sainsmart to everybody !