They only made about 3500 of these in both 9 mm and .40 S&W. If it's a different caliber than yours, then go for it. Maybe also, if it uses a different magazine than yours. Glock mags are more plentiful than S&W mags, for instance, since compatible Glock factory mags are still in production. You could leave one completely stock, and put, say, a Red Lion Precision forend on the other. As far as I know, Red Lion still makes, or can make, the version for the Sub 9.
By the way, they're aluminum, not steel, unless you or your buddy has one of the about 10 that were made in .357 SIG, which would be a collector's item. (One actually turned up a while back on this forum. They were a slightly different design with a longer receiver.)