When I bought my MM-211 it came with a defective M100 gun. Actually it was just a defective liner and after a quick phone call Miller sent me a replacement liner. As soon as we determined that the M-100's liner was bad I pulled the gun off of my old MM-140, which was an M-10, and used it on the 211. So I had both guns side by side. They were really quite different. Most noticeable was the cable support at the welder end, which is a much more substantial unit on the M100. As I recall the M100 was notably more substantial just about everywhere I looked. For whatever its worth I see both guns for sale on EBay every day for around $100 in "like new" condition.