p.hawksI have a gopro 4 black, and I personally wouldn't go for it.
You can carry just one device. The option for multiple lenses (if you go for that option) also seems pretty cool. I was also surprised to see that they have a decent amount of accessories. Lastly, price. It is substantially cheaper than a gopro (assuming you already have an iphone).
Iphone cameras are good, but not as good as the gopro (at least the 4 black). Weight could also be an issue, and using it looks a little unwieldy. It looks much less sturdy than a gopro case, especially the screen cover, I would compare it to a lifeproof, not a gopro. It is only waterproof to about 33 feet. I haven't gone much deeper than that, and many people won't go close to it, but it is worth considering. Editing could also be a bitch. On one hand, you can do it right on your iphone. On the other, the actual workflow could be a nightmare. No sd cards for iphones, everything probably has to go through iphoto/equivalent. Every time you want to put the videos on your computer, you have to wait for multiple gigs to go over a usb 2.0 connection (painfully slow).
The biggest turn off for me though is that it is on your phone. When I had a 5s, it was hard enough to keep the thing warm enough to stay on while in an inside pocket of a down coat. It would still lose charge fast. When it gets cold enough, they just shut off. Mine would shut down even when it was above 50%, and when it finally warmed up it would have plenty of battery, sometimes more than before. It's a cool idea, but if the idea is to simplify everything to one device, it seems a little backwards if you need to buy external batteries to be able to use it, which it looks like you couldn't use with it in certain mounts, and that is if you can even keep it warm enough to stay on.
If you don't see those as major issues, then it looks pretty neat.
Yeah I thought about it and it just seems like more of a novelty