I recently had a friend help me rebuild a 2007 RM 125. He said that "back in the day" Bill's was unparalleled. He was correct. The only negative is that the "works" pipe is very susceptible to rust. It takes a lot more care to retain it's luster.
Bought this combo for my 2015 yz 250 . Fit perfectly. Very good throttle response. Hits hard and quick .pretty good over rev.