Welcome to the website of a small indie iOS app developer. It's a bit of a work in progress at the moment.
Buchen is a bookmark manager for iOS that allows you select specific browser to open your bookmarks in. It has the ability to import your bookmarks in a nice JSON format and export your data in a nice JSON format or the standard HTML bookmark import format.
Have a look at the 'help' page in the app (found under the ... More menu) to read more about the functionality provided by the app and the browsers the app supports.
Unfortunately, it's not that straight forward to allow people to select their own browsers. They have to know the app's URL scheme and unfortuantely not all browsers use their URL scheme in the same way. However, I'll soon add a way for people to suggest new browser options.
In the meantime strictly speaking the safari option is the 'default' option and assigning any browser to your default will cause the bookmark to open in that browser.