This short book contains interesting mechanics for applying undersea exploration and combat to Fate. There are rules for various types of submarine and how to treat damage in terms of conditions (specific problems like damaged life support) rather than consequences or generic stress. There are three pages of write-ups for several locations in a near-future setting where ocean mining and undersea bases are common. I like the suggested skill list as a good starting point for science-fiction Fate in general. The book also has interesting rules for applying teamwork/morale to a crew's performance, which encourages the character interaction that makes a ship-based SF story like Firefly or Star Trek so interesting.
There's not a whole lot of material to go on, either in terms of "fluff" or "crunch". For instance, we get lists of specific damage conditions, but the rules for the rest of sub combat are half a page long. Combat aboard subs gets two paragraphs and a nice illustration. No suggested seabase/sub layouts even in the deliberately vague Fate style. There's basically two pages of setting backstory and three about specific sites. To use this book I'd need to do most of the work in designing the setting.
The character writeups and sample adventure deserve special mention. There are six pages devoted to a sample crew of six, not counting two more half-page illustrations. The adventure is eleven pages long, of which seven pages are also full-page character sheets consisting half of illustrations. This total means that most of the sample adventure and a large share of the whole book is just a list of characters -- which your players won't want to play as, since they typically like making their own. I would have liked, say, another three pages about places to go and things to see at the cost of losing some sample crewmembers, cramming two descriptions onto a page without pictures, or taking the D&D/Pathfinder route and describing a few people in terms like "5th level Lawful Good paladin of Soandso".
Are these really great characters, then? No, there's a weird focus on filling in diversity checkboxes. The adventure's villains are a white man, a white woman, and a maybe-white man. The heroes are a Hispanic woman, a Hispanic man, a biracial man (explicitly stated for two of them because it's important, apparently) and a "petite, nonbinary-identified person who uses they/them pronouns". The sample crew is also diversity-focused, including an Asian woman (?) in a wheelchair. Trifecta! Now, Fate rules are about having interesting character aspects that can be good or bad, so this last lady has an aspect like "Wheelchair-Bound", right? Nope, it's nowhere on the character sheet. So either the writer and artist didn't talk, or somebody said, "We must promote maximum political correctness by including a differently-abled person where this has zero effect on their physically demanding job in a confined space!" If you're going to have characters' tribal identity and appearance be so prominent, write that into the setting and mechanics like an RPG like "World Tree" or "Hc Svnt Dracones". Instead, this kind of design goes beyond inclusive into just plain silly.
So, there's some merit to the book, and it's cheap, but you could also get much of the benefit just from looking at the Fate System Toolkit (free online).