Just to support what has already been said. You spend weeks, months or more and £xxx building your pride and joy. Do you then sit back and think, hmmm, I'll save a few quid and risk the lot on a suspect piece of gear.
I have to admit that I've had two of the cheapo speed controllers, I bought them out of curiosity to run a pump bow thruster, a non critical system. They were laggy, impossible to control to my satisfaction, and failed very quickly.
Naturally, you will hear about people who have bought them and been perfectly satisfied, but it's a lottery, and not many people win those.
Chas