Unsurprisingly, Savage Worlds: Science Fiction Companion is…a companion to the Savage Worlds rule set. This companion helps add the sci-fi candle wax to the Savage Worlds mold. It accomplishes this task quick and snappy-like. It was easy to toggle between the two guides, and the Science Fiction Companion was slightly better organized. I recommend getting the PDF version of each one, so you can use that sweet, sweet Ctrl + F. 

My review of Savage Worlds: Adventure Edition: https://app.thestorygraph.com/reviews/e6dd4240-6d32-4195-9909-8526e4228f10