I use the super shelter on my HH Expedition model. My setup consist of the under cover and underpad (I don't have the overcover). I have used it in sub 20 degrees F with a space blanket between the hammock and pad and a 20 degree sleeping bag. For me the system works well and there are many people here who use it. It is a little bit of a pain to get into the hammock if you have a traditional bottom entry HH but not too bad once you get use to it. The temp rating for the HHSS I think is more dependent on the user because some people tolerate cold better than others. You will find some folks say it only works down to 32 degrees for them and others say they can go much lower. It also depends on what else you are using (clothes, sleeping bag, etc...).
Hope this helps some.