Curved end-links have to be made for a certain case in order to ensure good fit. The shape of the lugs as well as the distance between case and lug holes dictate this.
If you're lucky, you may be able to get generic end-links to fit with a lot of fettling, but it usually looks rather crude.
Wjean's bracelets are mode for specific watches, so they usually fit very well. What watch are we talking about?