The Super Shelter requires less protection than an underquilt because the protection is already there. The undercover is waterproof which presents some potential problems for condensation, thus the need for the space blanket. The pad is very light but bulky. It can seem a bit fragile but it works fine with a few holes poked into it and it is the cheapest piece of insulation to replace except for a blue Walmart pad. I've been down to 12* F with mine when combined with a 0* cheapo Coleman sleeping bag and a good balaclava.
I'm not dissing on underquilts. For the money, which for me always a factor, and the amount of use it gets in really cold weather the Super Shelter made more sense. There is a learning curve but it is not terribly steep. I leave the undercover on all the time and pack the pad separately. That way it fits into a #4 snake skin.