OsmAnd is the Swiss army knife of Open Street Map frontends, but as I'm sure you'll agree on (if you've used it), it can be a bit of a headache setting it up, as well as getting familiar with it.
Organic Maps caters more to people seeking a pure alternative to Google/Apple Maps. It's the layman's alternative.
If you're a poweruser, and already familiar with OsmAnd, there's no point in switching. But in terms of getting other, non tech savvy, people to switch, it's a great recommendation!
Just don't try to install Steam...