A few things about that insulation. In the photographs on the site, the insulation has been spray painted pink so it stands out and photographs better (and to make you think it's "The Pink Stuff" or something similar). What the insulation actually is, is the silver Reflectix insulation that you can get at Lowe's. Same exact stuff. Seriously. They add a few small squares of double-sided tape to the "back" side and that's how you stick it on.
When used alone with no foam board or canned foam insulation, and stuck directly to the metal skin of the van, it has an insulating value of about R-2 to R-2½.
Along with the Reflectix, with the addition of foam board (R-3.7) and canned spray foam (R-7 to R-8 per inch) to fill the voids, the R-factor of the insulation becomes somewhere between R-8 and R-17 depending on how much of what is used and where, with an overall average of about an R-12, maybe higher.
Professionally applied spray foam, and then Reflectix on top of that, will have the R-factor somewhere between R-17 and R-25.
The amount of Reflectix, foam board and canned foam, plus foil tape to seal the seams, plus Liquid Nails and/or 3M spray 77 or 90 adhesive, will set you back some money, but still less than the pre-cut insulation at that site, and it'll be far better insulated. All you need is a pair of scissors, some patience, and a few days to install it.
As for the site, it has a long and infamous history which is chronicled at the two major Sprinter forums on the Net. They do not have online ordering, you must print out the order form and fax it to them, and then mail them a check. They do not take credit cards (because you can contest a credit card charge when you're sent fraudulent crap, but you can't contest a check). The list goes on and on. The general consensus is, well, they're not highly regarded, I'll just say that. Over at the Sprinter-Source forum they have an entire forum dedicated to "Supplier Info, Reviews and Experiences," and SprinterAccessories gets hammered without mercy pretty regularly.
You're much better off with a tried and true, proven source for Sprinter accessories like
The Sprinter Store at Upscale Auto, or
EuroCampers. I and many other Sprinter owners have dealt with both of these places with no problems.