We just returned from our trip and I have to say I never noticed one of those kiosks anywhere. Of course I did not go out of my way to find them, but they must not be too obvious.
We do not have smartphones that can run the
MDE App, but I have an Ipod Touch. I have to say, that was the best thing to have with me this trip with the free wifi. We needed to change things and replan things all the time and I cannot imagine having to find the kiosks. And if they are as the above poster said, only for that day in that park....

That would have been horrible.
We were able to change FP+ selections for the next day with the app with no problems, even headliners. Changing the day of for headliners (even early morning)...nope, no times available. We were able to change the others with no problems even minutes before. FP+ for BOG was great, we did that several times on site. Very easy to get another one for later in your trip. We had no problems with MB for FP+, even just walked to something else when Space Mountain went down and scanned with no problems. Just told them that SM was down and we wanted to use our FP+ at that ride. No problems getting FP- legacy paper at all, no comments or trouble etc. We did not do that much as wait times were very low for most anyways, but a few times it was needed or better planned out that way to save touring time.
DH's Magic Band did give him problems on park entry a few times, nothing major but had to try and retry to get the green go ahead. One time they had to scan his KTTW card. I never had this problem but it didn't seem to like DH's. We learned by the end of the trip a trick to that. If you just tap your magic band on the mickey head and it turns white and starts to spin, you do not have to wait for it to spin spin spin and turn totally white to then put your finger on the scanner. If you tap your MB, have it just start spinning white, then put your finger on the scanner, boom = green. After we figured that out, his MB would work first time.