From what I've read, Parker's competitors sought to capitalize on the popularity of the 51 by introducing "almost" pens. Apparently, almost all flopped. The exception to that (according to Binder's articles) is the Waterman Taperite, which had a similar size and shape, slip cap and a partially concealed nib. The 51 had a fully hooded nib, and the Taperite had most of the nib sunk under the section, with a small bit of the nib exposed. I overpaid for a beater version of the Taperite because it had been re-sacked, and I'd read that restoring them was difficult. I also noted that this pen succeeded because Waterman made outstanding nibs, and for some of the Taperites, they had a bit of flex to them. Anyway, today I loaded mine up with J. Herbin 1670 Bleu Ocean and did some test writing. Happily, it does have a semiflexible nib and it's pretty fun to write with.