if thats what it would take for you to feel at ease with your LO playing down on the floor then go for it.
personally i wouldn't get one, have got 2 older kids and they've had their fair share of bumps, and lived to tell the tale.
when would yoou stop using it though?
My daughter (aged 9) fell down 7 concrete steps back in january and ended up with quite a hole in her forehead. (luckily it was glued together and there is little scarring) but my point is - accidents will happen at what ever age.
I've know of people to have to wear those type of helmets due to epilepsy etc, to keep them safe during fits, seizures and falls.
Nobody will think your over the top if you get one - your just doing everything you can to keep your little one safe. nowt wrong with that! Do what you feel most comfortable with hun xx