Killa Grilla is probably the best made after market grill grate you will find. They are pricey, but they are made of thick 304 SS and built to last. As long as you don't swing baseball bats at it the thing will probably last a lifetime. About the only time I have heard of SS thick grates not lasting a really long time is in a commercial setting. For instance the Weber Restaurant Ranch has a thick (probably 3/4") sear grate on the backside of the grill. The thing lasts months not years if I remember right. However, it has super hot charcoal running under it probably 10 plus hours a day almost every day a year.
I have a few of the Killa Grilla grates in the SnS style as I am not a huge fan of the smaller side flaps. I also picked up his charcoal grates for a few of my nicer grills.