My experience with the FarmerTec MS660 clone I bought off E-Bay is if your time is not worth much, you like tinkering, and replacing some parts for OEM Stihl, and you do not have the money for OEM, then the clones have a place. I posted a picture of my mis-drilled farmertec piston for a Husky 385, that I am still waiting on for a refund after 2+ years ... great customer service, NOT.
To get it to start and run properly more times then not, on the MS-660 clone, I had to replace the trigger group, I posted the obvious differences on the rods. I had to replace the clutch springs after one failed under light use. It was an okay purchase in total because I had to drop a tree about to fall on my house and it being 42+ DBH, I was not going to be using my Atlas 80v and my Husky 385 was DOA.
If i had to make a living with a chainsaw where my time and reliability does matter, it would be OEM Stihl, Husqvarna (pro saws), maybe Echo.
If you want to putz around and play around tuning and modding it, then it is a good choice, otherwise I would stay away from them.
I might buy a farmertec clone to use on my chainsaw mill, but, only knowing it will require hours of work and replacement parts before I even think abut using and abusing it. For my firewood processor where time is money, probably only a Stihl or make my own hydraulic saw.