We didn't use penny rounds for a backsplash, but they are what we used on our powder room floor. It's the only material in our addition that we wouldn't choose again if we had to start over. It was VERY hard for our contractors to install. Our tile came on sheets a little less than a foot square and it was extremely hard to get it positioned so that you couldn't tell where the sheets met. Also, because the tiles are so tiny (and round), the grout-to-tile ratio is pretty high. I'm not sure I'd want that much grout in a backsplash. I can tell you that it's nearly impossible to keep the powder room floor looking clean. Penny rounds are charming, but difficult. Hope this helps.

We used it on our entry floor and love it...However, it does scootch around and it is more difficult to line up than I guessed ahead of time. I would think it would be super challenging to put on a vertical surface.

Thanks for the feedback. Your comments have been helpful as you've pretty much confirmed my worries. I appreciate you both taking the time to post!! On to the next backsplash idea...