ios - Difference between internal and external testers in iTunes Testflight beta testing?

Question

Can anyone please explain in complete details the difference between internal and external testers in iTunes Connect Testflight beta testing? The difference here is just too brief. Does internal testers need to add UDID's of upto 10 devices? Or did apple completely removed UDID requirement now?

Can someone please explain what needs to be done to distribute and test app of upto 1000 users? If I have the clients iTunes Connect credentials, how do I share the app from his own account?

I know that there are too many questions asked in this thread which is against stackoverflow's policy, but i only need do's and don'ts of internal and external testing of this awful itunes connect testflight beta testing.

Answer 1

Internal Testers must be assigned the Admin, Technical, App Manager, Developer, or Marketer role in iTunes Connect, and you can only have 25 of them. You should review the iTunes Connect Roles. If you don't trust someone with these privileges, they aren't "Internal", they're "External".

You can have many more External users, but apps need to go through the App Store review process before these users can test them:

Apps made available to external testers require a Beta App Review and must comply with the full App Store Review Guidelines before testing can begin. A review is required for new versions of your app that contain significant changes. Up to 10 apps can be tested at a time, internally or externally.