$50 each is too high. You can get normal sankey kegs for $30-40, and ball lock kegs for $35-50. Unless you just want something unique, I'd pass...there are much cheaper SS options out there.
They are "old" in the brewing world. The only thing those are typically use for anymore are for cask ales by some breweries. Before the current sankes came about the Hoff-Stevens kegs were very common. So unless you want to do 1/2 barrels of cask ale I'd get something else.