You can always pose generic questions and ask for a show of hands. The problem is some people will be shy to raise their hand in public or may tend to follow the majority vote. Your results will be imprecise, at best.
You could also ask attendees to share their feedback or suggestions through a questionnaire. Only a few people will actually follow through. And by the time you collect their answers, your audience is gone. You lost the ability to ask follow-up questions and engage their immediate feedback.
You need a tailor-made, simple-to-use audience response system you can afford.