I believe Open fit earmold are used with open fit hearing aid
(highlands, your sig is remind me from Conan The Barbarian movie; see at bottom of trivia list Conan the Barbarian (1982) - Trivia so basically it was a Friedrich Nietzsche quotation )
I'm not sure what your loss is and what your audigram looks like. My ha had the slimtube option but my audi suggested a regular ear mold instead because you get more out of the amplification with a reg ear mold (if the mold fits properly of course)
I tried open fit and it definitly didn't give me enough-I have severe loss in both ears. So I now have really deep ear molds and they work much better for me, I was surprised by the huge difference
I would love to get open fits. But I can't take it because my doctor said it for mild or moderate hearing loss. Regular earmold is for Serve hearing loss. Many hard of hearing still wear earmold with BTE. It's big difference.