Asking a Recommendation from a Professor?

Hello,
For the last few months, I have been working with a professor, writing exercises and quiz questions for his online course. However, we always worked online (we live in different countries). He knows my mathematical capability well (because he both knows how successful I was while taking the course and how hard I work for writing new questions). Now, he told me that he could write me a letter of recommendation, and my question is that should I ask him to write it?

If he can provide something about you your teachers can’t, go right ahead. However I’m sure all your teachers know you are great at math, and have the additional physical interaction with you to write about your persknality and character.

Seems to me the prof. can write two types of LORs depending on the circumstance:

If you had the professor for a class (especially junior year) he/she could serve as a nice teacher LOR since he/she seems to know and trust you in a capacity beyond a typical student.

The professor could also serve as a supplemental LOR if he/she focuses on things that would not be found in a typical teacher LOR (notably your work helping him/her with the class – things like your work ethic, creativity, ability to handle responsibility etc. ). If you want to use the prof as a supplemental LOR be sure the schools you apply to accept an extra letter.