I purchased the back and sides protection only (there is no bottom piece), and using the gel made the back installation very simple. I had a couple small bubbles after removing the excess gel out. By the end of the following day it seemed perfect and the bubbles were gone. The sides were a bit of a hassle for me to install, but I managed. I'm glad to see 2 sets are included!
The only thing that should be considered to improve the skin (imo), is to make the back protector cover more of the aluminum.