Generally, I agree, it isn't very complicated to understand. But, it's very easy to forget to buy a C ticket if you're used to hopping on the U-bahn with your monthly AB ticket.
If you use the bvg app it tells you which ticket you need for any destination, but non-locals might not know that.
I don't know the BVG app, but if you're not regularly in some city installing an app, finding out how it works, adding your payment info is a huge hassle.
We need a single app for all German transit, that is well designed. Instead of hundreds or thousands of apps for every city and village.
What I also really liked is the chargeable chip cards in Taiwan. You could enter and exit anywhere.
Your card is charged with exactly the distance traveled.
No thinking needed. Short distances are always cheap. E.g. if you travel from zone B-C but start just one stop before B ends, you wouldn't pay for the whole of B. You just pay what you use, which is fair.
Not on all lines. If I remember correctly, I have only heard it on the new announcements for the BER airport. And, they actually tell you on time so you have a chance to buy an extension ticket.
E.g. the "new" Munich airport, all Paris airports (though you could argue that it's Paris which has unusually small city limits), Glasgow, London Gatwick, Stansted and Luton, San Francisco, …