As already said, there's not a lot there to help protect you, in a worse case scenario. Yes, many others aren't much better ... but there is better!
Ditto on the concerns re highway driving. I drive an ML, and even on windy days, I can feel the wind hitting it. I often wonder if Smart's and other similar mini cars, would blow right off the road! At the least, gaas mileage would be sure to drop, as it fought winds.
When they first came out, and I was getting my new ML, I asked the dealer about it. He said, he saw them as an enclosed golf cart and something or Senior's as a run-about in their gated community! Being someone who was selling them and saying that, his comment has stuck in my mind.
BTW there was a remake on the original design and engine a few years ago. Be sure you know which you are getting and whether it has maintained it's ratings with the new specs. Friends had one ordered at the time, and when they found out about the remake, they cancelled it before it showed up.
The only way you are going to really know if it is for you, is to go the distance to your nearest dealer, and give one a try. I'd want to rent one for a week or more, to give it a better fair try!
Good Luck ... getting a new car, can be very stressing, and too, a lot of fun!! :)