I bought the helmet when i started working on inverted airs. This thing definitely saved some concussions and the straps mold to your face real well. As for the sizing, i referred to my old football helmet size and it was spot on. If you don't have something like that to reference break out the measuring tape!
The helmet fits well. Keeps my head warm regardless of the temperature. I like the option of being able to put in headphones. The slight visor is also a nice look, it helps with ventilation for the goggles. As a general guideline I recommend bringing your goggles with when trying on helmets.