You know, it isn't JUST for the browser, several homebrews use the RAM in it, also you'll be able to play GBA games on your DS..
so i say it's worth it.. for only about 20$, you'll get all that.
and no, there aint no other ROM you can use, because that's the only browser released for NDS.
though, there IS other homebrew browsers.. but they don't support images, javascript and other basic features (DSOrganizes browser supports very small images) the only thing that's better with the DSOrganize browser, is that you can download stuff in the browser.
there are other homebrew browsers (like DShobro, Bunjaloo, etc) but they're inferior to the official Opera Browser.