Here's my review of these Fitsok Hikers. I bought 3 drops (9 pairs). For reference, I also bought 12 pair total of the Darn Tough hikers in 2 previous drops. First off, if anyone would have asked me a few months ago if I would EVER invest ~$220 in socks in a few months, I would have told them they're nuts!
I live in FL, so I'm hiking 12 months/yr. At the beginning of this year, I locked into hiking ~10 miles every other day (~150 miles/month), and I quickly realized that my sock inventory was not prepared to handle the rigors/risks of inadequate sock protection.
Over the last decade I've worn over-the-calf Smartwool PhD's under cowboy/work boots, and Merrell/Carhartt socks with trail shoes (Merrell Moab Ventilators lowtops/Geomorph Blaze Mids, North Face low tops) as well as a few pairs of Hoka running shoes. But ~10 mile hikes quickly proved the Merrell/Carhartt socks inadequate and I had a rash of blisters.
Enter the Darn Tough Hikers acquired in the first drop, and (thankfully) my blister problems ceased immediately. As the weather warmed this spring, the Darn Toughs started to feel "warm"...not an issue with moisture retention, simply temperature. Since the Fitsok Hikers arrived from the first drop, I haven't worn the Darn Toughs a single day, and no blisters either. Bonus is they are also cooler on my feet (I've used them up to 80-85 degree days), so they've delivered the exact performance I wanted. Another bonus is the compression of the Fitsoks feels great through the mid-sole/arch of my foot. From my perspective, the compression really makes my feet feel better after each hike.
I have not experienced any moisture retention or lack of breathability that others have written about. In fact, with both the Darn Toughs and these Fitsoks, the moisture moves from inside both brands of socks outward to the shoes so much that the insides of my Merrells/North Face/Hokas all always damp afterwards, so I tilt the shoes toward a small fan for a few hours after every hike to insure they dry completely. For more reference, since waking up this morning I've worn the Fitsoks with North Face lowtops, walked 4 miles to my local fitness club, lifted weights/worked out for 90 minutes, walked another 2 miles, and have have continued to wear them for now a total >12 hours (and won't take them off for another 4-5 hours), and they're still comfortable with no moisture retention issue. And remember, this is FL....already warm and humid in mid-May.
As for sizing, I bought size L in the Fitsoks, and wear size 11 in everything except the Moab Ventilator lowtops which are 11.5. Yes, the Fitsoks feel a bit tight to get them on, but that's the compression working. I have not felt any rubbing in the toe areas that some appear to have experienced. One thing, not really an issue, is the Fitsok hiker height is a bit taller than I prefer for lowtop wear (with shorts), so I roll the cuff down (doubling them) to just over my ankle. Again with no moisture retention issue with the fabric doubled there. The compression in the fabric is strong, so once turned down the cuff never budges during a full day of wear
Finally, as a test of the both the Darn Tough and Fitsoks durability for long-term use on trail hikes, I only used a single pair of each brand for at least 3 weeks in a row (that's >10 hikes totaling >100 miles). After each day's hike, I would turn each sock inside out, drape them over a chair arm and simply let them air dry until my next hike 2 days later (not in front of a fan). Actually, within ~12 hours, both the Darn Tough and Fitsoks would always be dry, and remarkably smell-free. This seems to indicate a single pair of either brand should be able to handle multi-day hikes without laundering, provided one can allow air-drying overnight. And each single test pair in both brands looked brand new at the end of the test
Bottom line, my Darn Toughs are in the drawer waiting for cooler weather to arrive this fall. I couldn't be more pleased with the Fitsoks, especially the price/performance ratio. And while I've had great service from Smartwool PhD's over the years, I have had holes develop in a few of them over time periods I would describe as premature. So from my experience, t hey don't approach the price/performance of either the DTs or the Fitsoks.
If I absolutely had to rely on a single pair of socks for a few hundred miles total of daily hiking over a month, I'd favor the legendary, apparently/supposedly indestructible Darn Toughs. But I also wouldn't hesitate to take the same journey with a pair of Fitsoks on my feet and another in my pack.