Interesting discussion, let me toss in my 2 cents. When we got this Hunter it was our first boat with IMF and was one of the features we were looking for. I'll pass here reading off the whole wish list but it was based on new physical limitations put on the Admiral. When we took delivery we had what turned out to be very unrealistic expectations of the IMF system. It was not trouble free, easy to use, convenient or stress free. It was exactly opposite of all of those things and frankly, it pissed me off that we paid a premium price for the boat AND sold what I had hoped to be our "last boat"(another story for another discussion). What we ended up doing was 1. talk with other Hunter owners in our club and ask what we were doing wrong. 2. called the broker and former Hunter dealer and ask the same question. 3. dug through all the paperwork on the boat to find the spar manual for tips. What we found was that we had "assumed" the previous owner knew what he was doing setting up the rig, he did not. The other Hunter owners had IMF, but a different brand spar, so they were only a little help. The broker was more help and called his rigging guy. Finally, buried in the pile of papers in the canvas Hunter bag were two things, the manual for the spar which was totally useless and an addendum to the useless manual. The spar was originally designed to have a traditional rig, sail storage on the boom. We were told that so many people requested IMF the spar maker modified the current mast and added the foil and furling mechanism. HOWEVER, if you followed the instructions in the manual for tuning the mast, you were done, that IMF mechanism would never work........and it didn't.
The end of this story is that we found this to be a very sensitive rig. If the main halyard is too tight or too loose, it affects the mechanism. If the rig tuning is not to the specs in that addendum, there is too much pre-bend in the mast and the IMF will not work. If you don't put tension on the outhaul when furling the main, the sail wrap isn't tight enough and will jam in the mast. So, I bought a LOOS gauge, read the addendum carefully a couple of times, re-tensioned the standing rigging to suggested specs, played with the main halyard tension doing an inch tighter, an inch looser, etc. and ended up with an IMF system that now works ALL the time.