Another issue to consider for China e-channel is China's disallowance of dual citizenship. There is a lot of discussion for how Chinese citizens who also hold foreign passports to deceive or circumvent the system, and one of them is to register for e-channel so they don't get questioned by immigration. So perhaps they flag certain people, or perhaps it's random, and if the operator sees that you're obviously not a candidate for dual citizenship, they just punch a few buttons to let you through.

Based on the discussion on this reddit thread: https://www.reddit.com/r/PassportPor...tes_now_can_i/
one of the key issues is that entry via e-channel by a dual China-foreign passport holder might be fine, but what to do upon exit? China checks passports on exit as you know, and if you travel to a country that normally requires a visa for a Chinese citizen, what do you do when you show them a Chinese passport? Personally this issue isn't relevant to me as I don't have a PRC passport, but again it's an interesting intellectual exercise.