I have the Leatt dbx 5 helmet for 6 months now and love it. The sizing is spot on. I measured my head circumference and bought it on-line. At first it's quite hard to put it on and get it off but in time it loosens a bit. Once I put it on, it fits great, doesn't wobble or bothers me a bit. It is well vented, great build quality and has the turbine system(similar to mips). I also have the leatt 5.5 neck brace and they work great together, obviously. One thing u should know...it doesn't have a quick release buckle. Leatt uses double D style strap as they think it's the safest, simplest and most durable system. The downside of this means it's difficult to operate with gloves but i got used to it. Hope this helps.