The Disney boyfriend and I were onsite in September last year and had an extra FastPass+ or two to book on a few of our days (some of the members of our group decided that they didn't want to join us, so we ended up deviating from our FastPass+ choices and ended up with extras
), so we attempted to use the FastPass+ kiosks. It was not a great time.
We only had experiences with them later in the afternoons, so this may not be the case first thing in the mornings, but there were always lines, the mounted tablets that they used were often extremely overheated and therefore slow as molasses, and the choices for FastPass+ attractions were often the less popular meet n' greets or attractions that didn't have wait times to begin with.
We were there one evening for MNSSHP in late September and the lines at the Tomorrow Land kiosks were honestly upwards of 30 minutes.
As I mentioned we had no experience with them first thing in the morning - but I'd suggest sticking with the My Disney mobile app, or booking in the hotel the evening before with the free wifi. Better than taking your chances with the in-park kiosks.
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No trips planned currently... But we're hopeful something in 2017!!!