Thanks for the info. I have 3 (5) gallon kegs now. I have a little space left in my keezer, but due to the shelf that is in there, a 4th 5 gallon keg will not fit. But a 2.5 or 3 gallon should because of the height restriction I have.
I've accumulated six 2.5'ers of various makes but I've bought them all new as cheap/used are so hard to score. Sometimes you can find new ones on sale, but "sale" is usually still pretty pricey. As mentioned AIH sometimes has used but IME they are always pin lock and usually go fast.