Unfortunately, we have no choice except to ride paved roads, and there is little chance for a problem except the rare possibility of collision. We do not wear helmets, but if we were on trails where rollover was possible, we would probably change our choice.
I did research helmets just to have one if we need them, and I came to the conclusion that the weight of the helmet is very important. I had a motorcycle, and the helmet gave me a pain in the neck. Try to wear one around the store for a little while to judge your comfort level.
Any helmet you buy should be DOT approved to meet the requirements of any trails that require helmets.
Considering the safety factor, it is hard to suggest not wearing a helmet, but we don't just from a comfort standpoint.