It depends of your head shape. I personally found Charles Owen helmets big and bulky with very little ventilation. Not to mention constant headaches due to my head not being the right shape. Charles Owen helmets seem to fit oval heads the best. They do rate very high on safety standards though, which is why they are popular for eventers.
Personally, I hate them. But it definitely depends on your head shape, if you have a ovalish head Charles owen is a better option and if you have a rounder head then stick with a Samshield. I prefer my Samshield over and other helmet, its so comfortable and way more breathable and ventilated than Charles owen