Fire pit inner ring. Purposes and can I make my own from a barrel cut out?
(edit Most barrels...) won't last very long as fire pits. I know this from burning trash when I was a kid. By the time the barrel was full it was falling apart. I never counted, but I would expect it to work well for about 10-20 burns and maybe 50-60 burns before its paper thin and falling apart.

Edit: The thickness of the metal is what matters. 18 gauge drums are what I find to be the industry standard; 18 gauge won't last very long in my opinion. A thicker drum would last longer. I personally own a fire pit object that is very thin, which probably would not last more than 10 burns. So it goes to show that any ol' manufacturer may not necessarily make a decent product. 

I have seen barrels converted to wood stoves. I have seen some of them fall apart and I have seen some stand for decades. This is due (primarily) to the thickness of the steel.

Edit2: Product reviews are probably important when you can't get the actual specifications. Amazon has reviews for the example product that you linked... 3.5 stars is not so hot.