There should be UI in the app to share arbitrary URLs. The bookmarklet works fairly well on a desktop but will become less effective over time as security restrictions prevent arbitrary code injection – e.g. currently you cannot use it to share a medium.com story because they have sensibly applied a Content-Security-Policy whitelist.
Added iOS because the bookmarklet doesn’t work at all there and iOS 8 provides the perfect mechanism for adding “Share in Newsblur” to every app.
I don’r appear to have access to add Android to the affected application list but it’d be extremely welcome there as well. I have a huge list of things I’d like to share from Chrome and Instapaper and it would be really convenient if there was a simple share action exposed by the official app.