I saw some american flagfish at my LFS today and I'm in love! I was told by an employee that they'd be compatible with my current stock...

pygmy cories
galaxy rasboras
cardinal tetras (I would re-home these for flagfish, however)

... but I was skeptical! Knowing all too well that I should do my research and avoid impulse buys... I came across some info saying they are peaceful, other saying they are too aggressive for community tanks...

Basically, what do I need to know about these beautiful killies? Thanks guys!