POP is awesome! I've been using it since they first launched. I don't work on many apps but anytime I do I always go with POP because it's so simple and quick to use. Love it!
Same here, I use it for very quick prototyping when I don't have time to go for framerJS.
Using Paper by 53 and POP together you can make clickable prototypes incredibly quickly. https://medium.com/p/64095daf7a92
I much prefer to do this in XCode. You actually can do much more things faster and with real interaction.
I like POP, but personally I prefer Pentotype.
It integrates the linked image idea with an actual sketching interface. I find it much faster to move back and forth between designing screens and linking them with Pentotype.
Yeah, it's kind of neat, and the tech behind it is cool, but are these things useful for anything more than ideation? By the time I want to use a clickable prototype I want to present something more hi-def, like sketch/ps + Flinto. Same reason I think Balsamiq is kind of useless. That level of definition is GREAT for coming up ideas, but, just on paper. That's just me though :)
A guy on my team is made high level comps in photoshop, then put them into POP to make the prototype.
Using it for more high fidelity prototypes can be done, and it's a pretty dead simple way to do it.
Pop helps me figure out all the screens I needed with quick sketches, and I could go back and draw one to add back in. Once I had every screen I need, I make the more polished versions.