This is one of those posts that if you ask ten different people, you'll probably get ten different responses. I have the HD unit on my Ultra and it works very well. It's cost was inline with the other coolers listed in this post, and it was relatively easy to install. One drawback, you have to pull the crank sensor each time you change the oil filter. The HD cooler has an insert that fits between the oil filter mount and the actual filter. This sticks the filter out about 1/4", just enough to have clearance problems. That being said, I have found that this aspect isn't any really big deal. The HD unit, like others, has a thermostat that opens about 185 degrees and is fully open at about 215(?). Hope this helps....