Awesome helmet. I bought a Medium from a separate store. Originally I purchased the Giro Air Attack, but returned it, so i'll explain why I kept this one over the Giro. (Both Giro and Bell have same sizing for these helmets Med in Giro = Med in Bell).
Similar to the Giro, the helmet features a Zeiss visor that magnetizes to the outside of the helmet (flipped upside down) when not in use. Although I wouldn't recommend riding with it up there, it's still extremely snug.
It also has a slider on the back that allows you to open and close all the vents (except the 2 on the very back below the BELL logo). This is more of a novelty and I'm doubtful it actually speeds me up in any noticeable way. I use this primarily when its below 65F outside because it does keep your head quite warm, and if my hair's somehow sticking out of the vents.
One of the main reasons I chose this was that it looks more like a traditional road helmet, especially if you leave the visor at home. The Giro looks odd in my opinion without the visor and even with the visor attached I felt it sat quite high (the bottom of the lens level with the bottom of my eye). The Bell still looks nice even with glasses, however I almost always use the visor. It has a large field of view and is surprisingly easy to wipe sweat off your head by pulling out the visor.
In terms of the negatives, relative to the Giro, I found the Giro felt more snug and comfortable. This was likely b/c it has a rounder shape (which is why i felt it looked strange on my head).
The Giro also had more replacement lenses for cheap ($40 on Amazon) and in a variety of more colors, where as the Bell only has a few I've found ($120 on Amazon only variants of gray).
I included a front/side view picture of mine b/c there's no stock ones out there.