Is the method outlined in the Flask Accounts and Authentication Lesson "good enough" to use for a paying client?

In the context of this lesson, is the authentication method that is being used good enough for a paying client? Or is this not professional enough? Would clients expect some other kind of authentication such as OAuth, or Google Authentication, or other?

If the client wants basic session based authentication, then yes.

If you intent to use Flask for an API, and have a separate SPA front-end, then no, you will need something like JWT:

Flask-JWT — Flask-JWT 0.3.2 documentation

O-auth is much more complex, you should not implement O-auth if the client only required basic session based authentication.

for a lot of these things, there are packages available.

Although flask is nice for learning, I would build client projects in Django. Django contains a lot more out of the box, saves you in writing a lot of abstraction. Which should reduce development time.

use Flask for an API

Does this mean an app that fetches any data using API calls like making use of Google Trends API?

You make it sound like Django is superior; from what I’ve seen, many sources do indicate that Django has a higher demand than Flask.

Well, if Django gets the most things done quickly, I suppose it would be wise to adopt (after having done the Learn Flask Course) especially since I want to maximize everything that I can offer even as an individual coder.

yea, if you have an SPA (single page application) or a mobile app, those use an API (application programing interface). In the most simple terms, an API means that the data can be accessed in a programmable way. Google trends is just one of the millions API’s in existence these days

superior is such an absolute term. I would make it a bit more nuanced: Django is a much larger toolbox while flask is more bare-bone.

The things you learn in flask you will mostly be able to apply in Django.

Learning flask first is a very sensible path, it will help you understand the tools Django offers much better