This is my Second Arai Helmet. First helmet was an RX-7 Corsair Harada. Crashed bad (I literally was rolling up and down the side of a mountain, frame broke in two separate places), thanks to the helmet (and other gear), I survived to ride again.
The RX line is awesome. Just like their predecessors, the RX-7 Corsair. Can't think of anything bad to say about Arai quality, fit, and style. The same quality as the Corsair V. Differences between the two are 1.) ventilation system (since the RX-Q is specifically made for the street, it provides better ventilation for stop and go riding.) With that being said, I don't ride on the track, nor have I used the Corsair V. But for $200 less then the Corsair V, that was the decision maker for me. 2.) The RX-Q vents aren't painted to match the helmet as opposed to the Corsair V. They are dark smoke plastic. But that's minor and the color is just about aesthetics. The RX-Q and Corsair V do share the same face shields and padding.
I have an XS and fit is perfect.
Of note, the only other helmets I have used are low end HJC's. So I can't really compare mid to high end helmets made by Shoei, AGV, Suomy, HJC, Scorpion and others.