A while ago we asked
Kyatric to thoroughly document the process of setting up IAP on Android and iOS. His tutorials are up.
From what I can tell the main problems are:
1) it's difficult to configure the IAP stuff on the dashboards - on both Apple's developer site and Google Play. These usually are set up for technical developers, and most C2 users are non-technical. On top of that it's difficult to keep documentation up-to-date because these services keep changing their web interfaces.
2) the build systems we recommend sometimes make it difficult to use the underlying Cordova plugins.
If you work around the issues, AFAIK everything works. I do agree though that it is too difficult. This is why we're rebuilding the feature and integrating it with our own build system for C3.