I have to slightly disagree with some posters -- I think fit is very much related to safety. A poorly fitting helmet won't sit on your head right, and thus can't be counted on to protect you in a fall. Because of this, I think it's worth spending extra if needed to get the right fit and straps that adjust well and don't go readjusting themselves.

Also, on the subject of fit: IMO, brand recommendations really aren't worth much, because helmet manufacturers generally make their helmets to fit either round-headed people or long-headed people, but not both. I've found this in ski helmets, kayak helmets, bike helmets, you name it -- a helmet can be a "great helmet", but if it's made for a round-head, it won't fit me worth a damn. Your husband has to put the helmet on his squash to know if it's right for him.