It's true that I bought it about 5 years ago and things may have changed since then.
But I think the sentence you're quoting is referring to the following: BC Navigator allows you to download maps for offline use from a variety of sources. Most of these sources are free (e.g. Open Cycle Map [related to OpenStreetMap], US Forest Service, etc) and some require a paid account with the map provider (e.g. CalTopo). So if you want to use the CalTopo maps, you need to pay CalTopo. But it's perfectly fine with the free maps.
The UI used to be pretty difficult to figure out. After a year I got used to it and it's fine. But they released a new version for iPhone which is supposedly quite different from the early Android version, and they claim they put more effort into making it easier to use.
Another thing that's very useful about BC Navigator is that you can easily import GPX tracks (e.g. planned routes) and overlay them on the map in different colors. So you can have your main route for the day, and maybe some alternate routes for a section where you're not sure if the original route is going to work out. You can keep an entire library of routes in the app, and select which ones you want to show that day.
It's just a perfect app for what I love to do - mountain biking in places where few people go.