Most interviewers don't have wear poker faces when they're not discussing salary. You can often tell by their response if they liked or disliked your answer.

Most good interviewers also have a list of questions they formulate based on what they think might be your potential weaknesses to assess whether they are a real liability or not.

So in a nutshell, if you pay attention to the verbal and non-verbal cues during the interview, you probably don't need to ask for feedback.