Inhumans comics don't sell at all. They're selling about 1,000 issues a month while all the X-Men titles are hitting at least 50,000.
That's not accurate. No comic sells 1,000 a month. The highest in the direct market for Inhumans is 25,000 and the lowest is 15,000 or so. That's direct market not counting digital sales.
X-Men have had an established at the top of the pack since at least the 90s. They should be selling among the best. That being said, Gold and Blue might be at that range, but Gen X, Iceman, etc. are comparable to the Inhumans sale figures. Not that it really matters since I'd prefer both to sell well.
BTW, there was another review that was apparently more positive, but it got removed, which makes me wonder if there was an embargo this first one broke. The review is also apparently based on the first 40 minutes of the first episode.
ETA: Gold 5 sold 54,000, Blue 5 43,000, Weapon X 4 35,000, Cable 2 31,557, Jean Grey 3 23,140, Gen X 3 22,220, Iceman 2 22,075. Black Bolt 2 is at 26,435, Secret Warriors 3 is 20,457, and Royals 4 is 17,007. It's a shame Al Ewing doesn't seem to be able to sustain sales because I love his writing. It's also a shame that Gen X and Iceman aren't doing better. I hope they find alternative markets to sell in.