The MM Navigator version costs less than Ozi & can import & calibrate images & 3rd party maps.
But if you're going to use free maps, why bother paying for expensive software? Why not use freeware, Orux for Android, TerraPerfecta or Quo for WM?
I've searched for MM chart torrents a few times but I've never found anything useful. There's a 2007 version of MM with some charts & a 2009 ozf image that's a screen grab from something like See You, not a CAA chart. Orux has a utility to batch convert Ozi files into Orux & it would be interesting to see if the Ozi scans are any good.