I’m using overlock for the first time and absolutely happy about it. It works perfectly and so easy to use even for me as a beginner who never used this kind of machine. I was surprised how good a cutter works with short edge. 
It came with 4 threads and I checked how to deal with it before I used my own threads. You can use 3 or 4 threads. I used 3 for cotton or not stretchy fabrics and saved thread. The result is still perfect. 
It’s really simple for everyone to use! I definitely recommend it!