I have been using Concepts for two days now, and, despite my limited knowledge of it, it has surpassed any other of the well known and recommended go-to graphic Apps I have paid for, downloaded and used (7 others thus far) for what I need it for: The replacement of tracing paper in my design process, in architecture and urban design.
The use of vector mapping, completely manageable layers and the ability to edit ANY line or object, changing its colour, weigh, "freehandedness", and opacity at any point, is unexpected, unique and only one of the features that is flawless, and puts this way beyond anything else I have tried out there, and since getting the iPad Pro and Apple Pencil a month ago, I have been looking.
Kudos to the development team. I hope this does well for you. You deserve it.