I think that there is one other big factor to consider in this--where you live. This is one factor that few people tell us when they post. If you live in a place where you have a short heating season and a long cooling season, something like this might be appropriate. But living in Michigan, I would have no idea since I sure would not want it here. Our heating season is the long one and I certainly don't want something that is going to reflect any solar heat back in the winter. Even in a place like Nebraska where you have more extremes of heat and cooling but the length of the seasons is about the same, this would probably be a wash and certainly not worth the money.
I hate to bring up something so obvious, but if your neighbors and friends are getting it done and raving about how much they are saving, it certainly might be worth investigating further and you can ask them for sources. But I would not rush into anything like this, no matter how good it sounds until you have the benefit of several years worth of experience with it's use in your community.