I too have a round head and the Shoei fit me well. Didn't matter which model, as long as it was a medium, it was going to fit. After five years, I retired my GT-Air. I really liked the internal visor. But because of that, the GT Air was never Snell approved, not that it really mattered to me.
The Quantum X are specifically designed for those who have a round head. This is the reason why I had to get the Quantum X. Their medium fits me well and is very comfortable. It feels very light , not heavy. Unlike Shoei, Arai does not make any helmets with an internal visor so all their helmets are Snell approved. They use a two visor system, the sun visor attaches over the main visor. The sun visor is pictured, I went with the mirrored red. Still trying to get use to flipping both visors up and down. For me, I prefer the internal visor. Honestly it was not easy attaching the sun visor.
Remember, helmets have a shelf life. After five years, the helmet is compromised. Becareful purchasing online or even in stores as they can be old helmets that has been sitting on the shelf for years. This is the reason why I had a 3 month lead time once I placed my order with Arai. It took time to make it by hand and then it had to be shipped to Arai USA and then shipped to me.
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