Guest Photo Sharing

I was planning on using a hashtag to collect our guest's photos but honestly wasn't sure how effective it would be with our crowd. Have any of you seen the app "The Guest" that the Knot has been promoting (it's free)? I'm not sure if many people would actually download the app and I don't like the idea of bugging them ahead of time to do so. The app recommends sharing guests' phone or email so that they can be reminded to download prior to the event.
Has anyone had success with either option or something else to collect all photos? If you aren't married yet, what do you plan to use?

https://www.theknot.com/photo-sharing-app/faq/#