At reading, one may be indeed hit at first by the most significant digit ('8' in your last example) that is somewhat useful, but the reader can't easily figure

At reading, one may be indeed hit at first by the most significant digit ('8' in your last example) that is somewhat useful, but the reader can't easily figure out digit's order of magnitude without reading the entire number. There's actually more. The reader can't spell the number right away, as it has to be read entirely and compiled in mind first. This compilation involves counting all digits in the given number to determine the number's size, then starting again by interpreting and spelling accordingly in its order each digit and its designation. This double-pass doesn't appear that efficient to me. On the other hand, if the number from your last example would be written backwards (452'392'8), its reading and interpretation would come efficiently in one pass ("four fifty and two hundred, three ninety and two hundred thousand, and eight million"). Even when all we're interested in would be the most significant digit and its order of magnitude, that would still be faster to determine (i.e. again, in one pass).