The differences are worth the separate books and it was due to them just having the Broken Compass rights sold...which they just got back a few days ago. They wanted to do something with the system but not just repeat Broken Compass, so they did Outgunned as their John Wick-style action movie RPG. The focus there is, as you might guess, high action and lots of fighting bad guys. They circled back to Indiana Jones and the Mummy style adventure movies with Outgunned: Adventure. The focus there is, as you might guess, lot of adventure and keeping your eye on the prize (the MacGuffin you're after) rather than John Wick-style shoot 'em ups. Both books are complete games unto themselves, so there's zero need for both unless you want both genres.