> Range voting is challenging because people often have difficulty putting an exact number on how much they want something, and also scales differ between different people. On a 0-10 scale, some people will be putting every candidate as either 0 or 10; others will always put in 3 and 7; and this depends a lot more on the voter than the candidate.

And, particularly, there is very notable cultural variation, which means (ab initio at least; over time, one expects behavior modification efforts would be deployed around this), support from different cultural groups in a diverse polity will have different electoral value even when turnout is the same.

> Approval voting is simple enough,

But also has the same problem: concretely what “approval” means is unclear and will be subject to voter-to-voter variation even when the actual preferences are identical.

No. I did my first exit polling in a small town in Texas and no one had any problems scoring the candidates.

Oops, link.

http://scorevoting.net/Beaumont.html