Helmets can and will protect you from impact of less than 20 mph falling from a height of less than a meter.

Any impact with higher speed or from a greater height and the helmet, no matter how expensive, won't make any difference.

Doesn't mean you shouldn't wear a helmet, just don't let the fact you have one make you take any risks you wouldn't take if you were bare headed.

There is some data saying that drivers give helmetless riders more space and slow down more passing you.

So, you helmet choice comes down to fit, comfort, ventilation and styling, in that order (my opinion only)

The Bern helmets are stylish and comfortable but not terribly well ventilated.

Catlike helmets are extremely well ventilated bu extremely ugly (again, my opinion only).

The helmet that you wear because it's comfortable and you think it makes you look good is the helmet to get.

Just don't expect that if you are clocked by a car going 40 or ride off a cliff edge that any helmet made is going to help even a little.

Having said that, all three of my crashes in the past 10 years or so have been exactly what helmets are known to be good at, low speed and no cars involved, and I am quite certain my helmets have saved me at the very least hospital admission and CT scanning... I was able to get up and walk away all three times thanks to the helmets. Had impressive road rash, of course, and in two of the impacts the helmets were visibly damaged.