How do extension methods work under-the-hood?

Question

A contractor where I work is using extension methods to implement CRUD on well-known internal classes that we own. I say it is better

Answer 1

Your question and the existing answers to it are all missing the bigger picture. New developers joining an on going project should conform to the existing coding styles and standards even if they're not the new persons preferred choices.

If a change in approach represents a major functional improvement as opposed to a primarily esthetic difference it should still be discussed and approved by the entire team first.

Once that's done the change should either be mass implemented and the style guide updated to only contain the new approach, or the old approach should be marked as deprecated and modernized as the code containing it is touched. In the latter case it's best to do commit the cleanup changes separately from the addition/removal/modification of existing functionality so that why the individual modifications in the diff were made is kept clear.