They produce crap work. I had a V6 in a ranger that I got a new engine for from them. Heads/valves were not done correctly, required a new engine after a few hundred miles, and they used a loophole in their warranty to make sure that they didn't have to cover the labor for replacement. I had heard horror stories about them before but decided to ignore that because the price was cheap. You get what you pay for in this instance.
I'm not an expert, but I play one on the internet.