Honestly, you have to go with your gut feeling. A lot of people jump the bandwagons here and hell I have even done it.
I use both SS and Fatmat and when I ran out of my SS product, I threw in the Fatmat on my back quarter panels where I have a big hole. Most people say don't go verticle with it or it will fall off with time. Well, I have had in there in some pretty hot weather now and holds up fine and has quited down what was my biggest rattle. I was going to put SS in there, but realized I wouldn't have enough, so said screw it. Don't rattle there no more, but on my trunk lid where I have just one layer of SS, I still get rattles pretty bad, no where near what it use to be, but they are there. My lid also never rattled as much as my rear quarters.
Not dissing SS, but I feel in my install anyway, that the Fatmat is doing just fine and will be doing my 4 doors and rear deck with it. I am confident in it now.
Remember, it's just the internet. So lets believe everyone else. Hell you don't have to believe me, I don't care. I may also even try some Peel and seel, if I run out of the fatmat. No sense in spending more money than I have too.
Will say if you have the dough, then yes, hit up the SS products. They work, but I just can't justify it enough to get more of it right now.