Exif Wizard-Pro

but needs to add an extension to the built-in Photos app to at least view metadata, and preferably edit it from there or have a link to open the app to the photo being viewed.

I use this app regularly for geotagging photos I've transferred from my regular camera, and it works well for that purpose. Two minor complaints which I hope the developer will address are that the iPhone and iPad versions lose in-process changes to a photo if the app is closed and reopened. The iPad version does not offer a hybrid view when geotagging using map search.

Really useful app to have when you need to read your Photos.

Gets that useful photo data

Just like the title says. Pro version has all EXIF, including Hipstamatic combo info--a huge plus. The other "unlabeled benefit" is the ability to A/B compare photos with it. (Around iOS 5, the native Photo app lost its forward/back arrows, making instant A/B'ing impossible. This is one of a few apps that works around that utterly needless and dumb 🍏 exclusion.) Highly recommended.