Stefano, see if you can try them on in store. If not, I would say, measure your foot like Bont's website states, but check your 2nd and 3rd toes. If they don't look like the image on the size chart (meaning they are equal length/longer than your big toe), I would say go up one size to be safe -- that's one size above the recommended 4-5mm over your actual foot length. The top view image is the exact shape of the shoe, so you can estimate how much less room the 2nd and 3rd toes will have in comparison to the big toe.
Other than that, I think the size chart is pretty true. I wish more companies would list the actual foot size in mm vs some arbitrary number like 8 or 8.5. I just picked up a pair of Vaypors in the size Bont recommended, and they seem to be half a mm too short on my 2nd toe, but we'll see how it feels after a molding session or two. Also make sure to mention if you have flat feet, if you're buying from Bont's website.
