I started reading Tales from the Frontier yesterday.
I'm running a big-ish site focusing on stories, fanfiction and the likes, and thus I get to read a lot of really bad, and some really really fantastic stuff. My experience with tie-in books for games has been disappointing most of the time.
I still remember the booklet that came with First Encounters, a game which I completely overlooked when it came out due to non-existent advertisement, and when I saw screenshots I had to have this game, even though it was already a few years old. And the booklet that came with it, well... Let's just say I still remember three of the stories in complete detail. They were that good.
Do the new books hold up to that standard? Well I can't say for all the books, and opinions on "Mostly Harmless" seem to be rather mixed. As for what I've read of "Tales" however, yes, this is both relevant to Elite Dangerous AND really solid SciFi. It's not cringeworthy like so many tie-in books.
Soooo yeah. If you are on the fence like I was yesterday, the people writing good things about Tales from the Frontier are right. It's a solid read and if you are a fan of the game you'll enjoy it even more, but that's not required to be able to appreciate.