Not for lack of progress per se, but one of them got very upset and angry when I did not do what he wanted and when I challenged him. I left him after this became repeated too many times.

I think it is normal and natural that people become frustrated for lack of progress, especially if they have invested a lot of effort. I don't think it is right for a therapist to express their personal frustration much though - it can easily make the client hold things back or try to act in certain ways to please the T more than for its own sake. I do believe it is impossible to completely conceal frustration at all times though and that's okay IMO - just try to make an effort that it does not become excessive and condescending.