"Attic foil is tough material, no issues with tearing - superior to cheap stuff at local hardware store. Easy to work with. My attic is walk up with flooring in 1/2, blown insulation in other 1/2. Insulation installation certificate claims R-30 and building envelope is well sealed (checked with thermal camera) except one duct boot (I'll get to this fall). Completed steep hip roof section by myself but would have been a lot easier with someone assisting. Remaining sections went faster with sons help. Instructions, online faqs, from this company are honest about what to expect in installation and performance. Had extensive temperature/humidity monitoring before/after installation. Located in Raleigh area, temps taken over mid summer. At peak of hip roof, not much difference (not important from energy savings perspective) but at top of insulation and attic floor late afternoon high temperatures were 5-12 degrees lower. More interesting, the temperature dropped faster in late evening/night - I presume because insulation may have absorbed less heat? Overall savings in electric is a bit difficult to quantify as youngest son moved out and some other minor improvements made at same time - reduced average electric bill by 17% BUT NOT sure how much can be attributed to barrier.
On interior, upstairs conditioned space now takes much longer to heat up with AC off during day, doesn't get as hot (~2-3 degrees less), and takes less time to cool in evening when we get home.
Assuming a home has adequate insulation and is sealed well, I doubt this barrier would have a reasonable payback if installed by contractor. For DIY, I believe it is worth the time and cost. Besides, it's shiny - who doesn't like shiny stuff :-). "