I used one, and it was fabulous.

SKnot saw us wearing our helmets all the time, so it wasn't too big a deal for him. We let him wear it around in the house, and we made a "helmet" for his stuffed rabbit out of a yogurt tub. He decorated the yogurt helmet with stickers.

He'd put the yogurt helmet on the rabbit, we'd put the toddler helmet on him, pack both of 'em into the trailer, and away we went!