Just anther datum for the thread: I had a Jewell fail-to-fire at a match after about 3000 rounds. It felt like something inside broke. I had to forfeit the match, then when I got home, I took it apart expecting to see broken metal, but just some grit and oily substance (probably cleaning fluid and bolt oil from the dozens of f-class matches it had seen).
I cleaned it up, reassembled/adjusted per Jewell and it worked fine for another 2000 rounds or so at which point I got another FTF at a match. This time I finished with a spare Timney that I now keep in my bag. The cause of this failure was that the pull-weight set screw came out. I later found the set screw and spring in my rifle case, so put it back with a little thread-locker this time. We'll see how long that lasts (it has outlasted 3 barrels).
Overall, I'd consider the Jewell to have performed well. It was my fault that I didn't keep it free of debris, and partially my fault for not checking the set screw (partially Jewell's fault for it losing its interference fit).