I have 2, both 660 clones. The first one I bought as a kit and put it together. If I remember correctly it only took 3-4 hours to put together. I put a different piston and better rings in right from the get go. The saw started right up and ran great. I used it for about a year of occasional use. Then last winter a friend of mine wanted to use it to cut up some big trees, it has a 36” bar on it, and it locked up. I got it broke loose and tried getting it started but no go. I took out the spark plug and can see some scoring so I am thinking it is low on compression. Saw number 2 came because I was lacking ambition with to many projects going on so I ordered the “pro” version and it came put together. So far it has been a good saw, I run a 24” bar on it. Saw number 2 doesn’t seem to have the power saw 1 had but that might be the reason saw 1 doesn’t run anymore, thinking it was running a bit lean.
Overall I think they are a good buy for occasional use but I wouldn’t rely on them for everyday.