In case it varies between countries, by thesis committee I mean 2-4 professors who examine you on your MSc research after you submit your thesis, so except for your advisor, they are usually not familiar with your work prior to submission. Some of them might belong to other universities/departments and not be familiar with the student at all.
I am wondering whether such letters would be valuable. On the one hand, I feel they should be the next best thing after letters from people you've done research with, but on the other hand such letters can only refer to the quality of the outcome of your research and not your character.
What about letters from professors who have read your papers/thesis but haven't met you in person and thus haven't held a conversation regarding your research with you?