Spent a week in Sardinia with SP29K-M. Hot and humid. Also worn them elsewhere but figured scorching Mediterranean weather was the real test.
They're... OK. Certainly as well ventilated as cargo shorts are likely to ever be, and despite being black I never felt they were warm or otherwise problematic. The length is certainly not too short; I'd feel weird wearing anything below my kneecaps in this kind of weather. But put anything heavy in the pocket and it peeks out through the leg opening which is... not a great look. The flimsy pocket material has held up well despite looking super fragile. Sharp keys etc have not messed anything up for me yet.
The belt fly works, but offers no real advantage over a regular fly. The little loop to put the strap through is a bit stupid since it's hard to tighten through that loop (I feel like I'll tear it off?), so I end up taking the strap out, tightening, and then often leaving the strap hanging more in the front. Threading it back through the loop feels like letting a mediocre design dictate my behavior.
The material is very easy to brush or wash off if you spill food or whatever, and remarkably they didn't pick up any smell over a full week of intense groin sweat. But not sure how it'd feel in longer pants, definitely feels like something primarily for shorts.
Are they worth the cost? Unless you desperately need this exact pocket configuration, I think not. I don't really regret buying them but could live without them. Probably using my veilance stuff more for the rest of the summer, but keeping these in rotation.