The more formal number ideographs are the original ones, the simpler ones were simplified so numbers aren't as awkward to use.

You can also easily change a one into a ten, for example. Note also that it's not exactly a positional number system like Arabic. E.g. the number 123 would be written 1 hundred 2 ten 3. IIRC you can also easily change a ten into a hundred or thousand, so for larger values with a few zeroes in between you could shift a meaningful place into the zeroes to the left sometimes.

Well, just look at the symbols in his comment. 2 into 3, 4 or 5 is pretty easy looking, as is 1 into 10, 7 or 8. I'm sure you could probably spot more.