On the surface the interface isn't too bad. It could be the basis of a basic quick and easy army builder tool if it weren't missing some key features. It lacks a strait up list view of the units you've added. It also has no way to edit a unit once created other than to delete and recreate it.
They say it's a collection manager, but its structured pretty badly for that. Collections don't always match legal unit sizes and composition. How do you represent those 20 extra plasma guns you have from the bygone days of 4th edition? It doesn't have a way to specify what version of a model you are using, Is it a 2nd ed Tech Marine model, or a 3rd ed Tech Marine? These are all the features you'd want if you where managing your collection of Space Marines collected over a decade in the hobby. And who gives a hell about points in your collection? My closet isn't limited to only holding 4000 points of Space Marines..
The UI is structured better to be an army builder, but with a few fatal issues in that regard. You can't set a target point size, your can't make more than one list, and you can add allies(not even allies from the same codex using another Marine Chapter). It's also annoying in that any new unit you create is not added to the point totals until after it is saved, and, as I mentioned above, immutable from that point forward.
Software is hard, and I pity the poor dev who had to develop this in whatever scripting support apple provides in their iBook framework. But this seems like something that should have never been advertised and released. It feels like some prototype a dev wrote as a proof of concept, and some manager decided to ship as a real product.
It's disappointing really. A fully integrated in codex army builder would be the killer app for digital rule books.