I bought a Z-1 used from DZ, sized per the manufacturers chart.
I'm 6'2" and have a 24" head so I needed an XXL.
The helmet looked nicely made, but fit my face really tight.
My nose just hit the inside of the visor, my lower jaw was pushed back and I couldn't talk at all (painful), and the sides pressed hard on my cheekbones.
It fit the top, back and sides of my head nicely - it seems that it is designed for more narrow faces.
Fortunately it was really easy to re-sell at the local DZ - but the purchaser thought that it had a snug facial area fit too.