It’s published by C & T Publishing and appears to be their Quick & Easy Quilt Block Tool in a digital format.
They have the tool for sale on their web site at $16.95 and this app was only $4.99, which seems like a good deal for a pretty useful tool. From what I can tell the app appears to be a complete replication of the physical quilt block tool though I did see a reference in the app to something on page 109. There is no page 109 in the app.
Good on C & T Publishing for monetising their content in another way and at a reasonable price.
Being an iPhone app it’s portable. The content is good and you get dimensions for each of five different block sizes at a touch.
The user interface could be better. In particular the next and back navigation elements to move between block types are not very attractive and are placed too close to the selectors for the different block sizes. This could have been implemented much more elegantly with a swipe gesture.
A feature I really like is the ability to save blocks to your favourites, so you can quickly scan the subset of blocks that you feel might work for your next project.
My rating: recommended as it can help you with visualisation and measurements, even when you’re on the move.