As a dealer, I've been very happy with it. It's technically more dense than the 1/2 lb foam... but I really don't think you'll notice that on your electric bill.
If anything, it makes the spas heavier to move... but that's an installer issue.
Basically... it insulates like full foam, but it's a loose-packed material. Which is really easy for our techs to work with in the event we need to.