I can't compare to Shimano having previously used Giro shoes but compared to those they are true to size. I am a UK 9 in regular shoes and a 42 in the Explore works. They are really comfy to ride in, I wouldn't say they are amazingly comfy to walk long distances in but that's about what you'd expect.
I recommend them, the only thing I have an issue on is the fact that they are perforated, to me this doesn’t really make sense given that they’re marketed to be worn in all conditions. If its slightly wet out, you get wet feet. Having said that I rode them on a little tour round Belgium last summer when it was disgustingly warm and they were great.