Michael Toyamawrote a review of La Sportiva Boulder X Approach Shoe - Men's on November 11, 2018
Familiarity: I've used it several times
Fit: True to size
I really love these shoes, but I'm going to have to sell them to someone whose feet run cooler than mine. In any temperature or activity level, my feet overheat in these things like crazy. Even sitting around the house. I gave them multiple tries on the trail, including hiking on a fairly cool day. I find these hotter than my goretex backpacking and mountaineering boots, which is hard to believe. It gets so uncomfortable I have to take them off mid hike. I do believe this is specific to me (hence the high rating), but I just want to warn anyone who also knows they have hot feet. The uppers seem practically impermeable to air and just don't vent. I'm going to give the La Sportiva TX3s a try, which look similar to these but have a lightweight mesh upper.
Aside from the hot feet, these perform amazingly well. They hike and scramble fantastically. I'd actually get excited when I put them on, knowing I could go flying up some rock off the trail with confidence if I wanted. They look good too. I really wish I could have kept them. La Sportiva continues to impress me and these would be my fourth pair - I own Tarantulaces, Trango Cubes, and Nepal Cubes. No other mountaineering boot manufacturer seems to fit my feet well, so I'm pretty invested into the La Sportiva family.
Sizing. Street and hiking boots, I am a size 12, sometimes going down to an 11.5 and almost never going up to a 12.5. La Sportiva is the only exception: I wear a 46 (12.5) in all of the above listed La Sportiva shoes, and the 46 Boulder X's fit me perfectly: fit was just a little snugger than my other hiking shoes, reducing slop for better performance on rock. Didn't negatively impact hiking. Any smaller and I'm sure I'd have issues on the trail.