I've tried a lot on, and this had amazing fit, was super light, etc.
I also discovered something ... I got my Quantum when I was just starting out, and didn't know a lot about helmet fit. I've learned a lot since then, so rather than just order another medium, I made sure I went and tried them all on again. I found out ... I should actually be wearing a SMALL helmet to get the proper fit!! After comparing S to M I was able to properly identify areas like the back top half of my skull where it was too loose - and we all know my feelings on that topic by now, so this was enlightening for sure.
My current one, which is beat up anyway, is a medium. And after realizing what I did today, I think it's too loose on me; it's a tiny bit tighter, but not much. It's also broken in, but still... So I'm done with trackdays until that bad boy up there shows up (probably going to have to get it special order due to it being a rare design), since I dunno what my current one is going to really do for me besides save a bit of roadrash.
However I'd rather discover these things this way, than the alternative.