Scroll down to the Natural Minor and Harmonic Minor harps and give it a read.http://www.leeoskar.com/harmonicas.html
Natural Minor and Harmonic Minor would have the same blow notes but the draw notes have different ones that have been changed.
Harmonic Minor harps give you the sound of traditional Yiddish/Russian/Greek sounding music where as the Natural Minor harps give you more of a sound like many Pop songs from the '70's and '80's.
If you can you really should get one of each and remember with the LO Natural Minor they're giving you the 2nd Position key, not the 1st Position key like you'd get with a "normal" Major keyed harp.
They also have a chart on the LO site that'll give you relative pitch for all the harps so you'll know what to expect. I love my Natural and Harmonic harps, they've really helped to spice things up and get me back into playing.