multiFEED makes grateful use of the exhaustive list of UserAgents compiled by Techpatterns from original research and crowd sourced updates. The UserAgents are organized hierarchically by platform, device, operating system, browser, etc., making it fairly easy to find what you are looking for. multiFEED reflects this hierarchy with a series of drop downs, each one more specific, till you get to an actual UserAgent string. Start by tapping the first blank drop down and make a selection. Continue tapping the blank drop downs that are revealed until you get to an actual UserAgent and the Select button on the action bar at the bottom is enabled. When you find one that you want to use for the feed, tap the Select button and it will be copied back into the UserAgent field on the Settings page. If you can't find what you need, or change your mind, tap the Cancel button on the action bar to go back to the Settings page without changing anything.
Remember, you don't have to use one of the UserAgent strings provided by multiFEED. If you have the UserAgent for a browser or device that multiFEED doesn't know about, you can always just type or copy it directly into the field on the Settings page.
The Techpatterns UserAgent list is © 2015, Harald Hope.