What is the fundamental difference between registering external Asterisk providers and which is better?

Question

Asterisk

Greetings, Comrades!
Those who know, tell me what is the fundamental difference, will I register an external number using the register line in general and the friend type of the subscriber, or without the register line with changing the type to peer and adding a callbackextension?
I tried both options, it works both ways, but which is more correct? For example, there are 5 numbers from one provider. The number, login and password are different, the rest is identical. How to properly register them with register or callbackextension ?

Answer 1

Doesn't matter. And that's how it works.
callbackextension picks up the necessary parameters from the section, these are the ones that you entered in the register line

Answer 2

If you have several trunks for one provider, or several SIP numbers in one trunk, then callbackextension will help solve this problem

Answer 3

For your information, Zadarma.com changed something a week or two ago that numbers stopped working for incoming calls, they were registered with the friend type. Fixed only by adding callbackextension.