I’ve owned a bunch of these in 700x35 used tubeless and 100% suffered from delamination from inside and excessive weeping through the tread. This was with a variety of different sealants and a couple of the tires
were warranty replacements for this issue which quickly failed the same way. They came from different suppliers every one had this problem so I do not believe it’s batch related. When I’ve used them with tubes they are pretty good.
I log about 2,000 miles a year, 85% road, 15% gravel and these are perfect! I'm currently running the 700x32mm on my Surly Midnight Special. I typically average 16-17mph and never feel the need for a dedicated road tire. I'm running tubeless and have about 1,200 miles on these so far with NO flats! I've used similar Teravail & WTB tires with less success. I will absolutely be purchasing these again once my current set wears out; I may spring for the 35mm variant next.
I was running 35mm gravelkings on my previous bike (for about three seasons) and have graduated to 43s on my new (higher-clearance) bike. I ride 75% road, 25% gravel with these (including some really rough forest service roads) and I'm convinced that these tires are the sweet spot--not just for me, but for most people. They're supple and fast, they don't puncture any more than other tires I've used, and even on gravel roads it's rare that knobs provide much benefit (imho).
Pair the 35mm version with the 35mm Tannus inserts. You get the best of both worlds. Supple ride with flat protection.
Took me about 3 days to mount the tire w/ the insert. Not for the feint of heart.
Worth it though because the Schwalbe Marathon Plus is the only 700c tire that can withstand Goat's head thorns out of the box. But those tires are hard as a rock and slippery in the rain.
If you don't have Goat's head thorns then don't worry about inserts