There is actually a hook built into the passenger seat for your helmet... more more secure too.
No offense but you're actually missing the point with this helmet hook.
The idea is actually NOT to be able to lock it or so. That's just an extra thing IF you want to do that.
I never bother myself.
The only idea behind with it was to have a secure place to hang it while you sit at the gas station, stop to talk to someone, etc.
IE, just to have somewhere to hand it without ANY effort like having to get off the bike, unlock the seat, unlock the lock and so on.
I have also dropped every helmet I've own and the 15 bucks are worth it not dropping or ruining the visor but above all it's so damn convenient.