NOTHING 1/4" has and R-Value of 22. Good info on all bubble foil/foam foil type products: https://bluetexinsulation.com/pages/r-value-of-bluetex-insulation
Man, compared to my attic this is a breeze. Just staple the attic foil to one end, push it through the trusses and have someone else pull it tight on the other end. Staple and trim and your done. It will hang a little between the trusses (looks like about 10 ft) but will work fine and not much...
It's hard to say exactly. The attic is a lot cooler. The main thing we had to do was Raise our thermostat 3º from 75º to 78º. It actually got too cold keeping it where we used to. So, I know that this alone is saving me money and the house is more comfortable.
Here is some good info comparing radiant barrier spray to radiant barrier foil. I installed the foil and it made a big difference.
http://atticfoil.com/radiant-barrier-spray.htm