I had the chance to test the limits of the HH Supershelter at this weekend's Ohio Hang at Wildcat Hollow.
Temps from my phone: 31 degrees @ 10:30pm, 25 degrees @ 6:30am
Low temp according to wunderground.com was 20 degrees.
Hammock: HH Explorer Deluxe
Supershelter: undercover, overcover, foam pad, mylar emergency blanket
Sleeping Bag: 20 degree synthetic bag (el cheapo from a yard sale)
Clothing: wool base layer, my regular hiking clothes, fleece jacket, balaclava, rain shell
Extras: 2 Hot Hands hand warmers
Results: While I wasn't especially toasty or even comfortably warm, I stayed warm enough to sleep through the night. No cold spots that I could detect. When I got up to water the bushes early this morning, I could tell a big difference between the temperature inside the hammock and the outside temperature.
Conclusion: I'll definitely use this system for temperatures down to, say 30-35ish and it should do the job quite well. It's also comforting to know that I can take down as low as 20-25 if I need to.
Thanks for listening.