I've been shopping at Fanatical for years, since they were Bundle Stars, and have bought numerous bundles and a handful of games from them. I consider them to be one of the most reputable Steam key resellers, and I can't recall ever having any issues, or at least any serious ones, with them. Orders are quick and easy, with keys being available within a minute or so. The Star Deals are usually pretty good, though I don't buy them very often, as I try not to buy too many games individually, preferring to just wait for them to be bundled.
The bundles are hit and miss, some being great, some average, and some that aren't worth it even for the low asking price, which is usually $1-5. Part of that is the quality of the games, and part of it is that, as my library grows, bundles become a less effective means to add to it, as I find myself already owning many of the games in them. Still, occasionally they'll do a bundle that has several good games I don't have, and even if there are only 2-3 good games, it's often worth it for the low price, and I can always trade the extras. But while I do wish they would put out some better bundles, I have no hesitation in ordering from them when they do offer one I want. And unlike Steam and Humble Bundle, both of which are reputable but don't seem to care about their customers, I don't mind giving Fanatical my money.