I've been running a Hayden M6 since 1998. The bike I was riding at the time had about 85,000 miles on it. I figured the original primary chain probably had developed tight & loose spots, so a new one was installed along with the Hayden M6. About 110,000 miles later I added one shim under the spring. I put about another 5,000 miles on that bike before retiring it. I removed the M6 from that bike, removed the additional shim, and installed the M6 in my current bike, and have put more than 25,000 more miles on it. It still shows very little sign of wear.
I hope the H-D unit is every bit as reliable since it is in the '06 Dyna's and all '07 Twincams.