Interactive poll during the presentation - worth the hassle?
When you say "lecture", I'm not sure whether you're talking about a one-shot talk (e.g., a conference presentation, an invited seminar), or about an ongoing series in a class.

While I personally have not taught this way, I know that there has been a lot of experimentation with having students answer questions during lectures with software in the way that you describe.  There, the idea is to have the students actually working problem as part of the lecture---essentially, a hybrid between normal and flipped classroom.  In at least some cases, this seems to work very well.

For a one-shot talk, on the other hand, I have a hard time coming up with non-contrived scenarios where I think this would be worth it.  Why would anybody be willing to install some random app for just one talk, and won't you lose time to getting them set up with it? What could you gain from an online poll that you couldn't get through a quick show of hands?  Once people have switched their attention from you to their screens, aren't you just encouraging them to check out and read their email / browse the web?  To me at least, the negatives seem to far outweigh the benefits.