I've got a Leatt Adventure. Cost me $500(?) about 12 months back, but I think they're down to $350 now.
Its feels like it will do the right thing - I haven't "tested" it yet, but when I swivel my head around, the helmet contacts it before my neck starts complaining.
I have absolutley no issues with the comfort side of things - its an extra thing to put on/take off, but I very, very rarely notice it when I'm wearing it. Actually, the main time I notice it is in the pits, when you're doing something like looking for something under the car seat...