I don't know or use it personally. But the developer behind it is very experienced and sells the nice, tried and true image editor Acorn here.
https://flyingmeat.com
I used FMDB in a number of iOS apps (although it's been quite a few years back) and it was a pleasure to use. It was simple, well-designed, and with no surprises.
In terms of usability it was lightyears ahead of Core Data, and it actually worked smoothly with multi-threaded apps without breaking down constantly (as had been our experience with Core Data). It was a joy to work with.