Mythical Shoe Sizes

I'm from England and I want some Mythical Shoes. I'm about a size 9 here, but American sizes are different. There is a size conversion chart on the Tweak website, but my dad doesn't quite trust it, he has experience of getting shoes from America that didn't end up fitting him. Should I go with what the chart says on the website or is it unreliable? If anyone could help sort this out i'd be really greatful.