I was approached by the recruiter who kept me warm through the process. I had initial screening and interview with the hiring manager but I don't think we got the click - the conversation was rather dry and questions not super deep so it wasn't a suprise when got rejected. I asked the other recruiter for some feedback and haven't heard from them never again. I think 2-3 sentences of feedback won't ruin anybody's schedule but only build positive candidate experience. So I really encourage you to provide the feedback.