I put 50 of these (1-1/2" - 2") into a large holding tank with a whole bunch of dollar size angelfish. They got along perfectly until I didn't feed them one day, and they decided to eat the angels (chewed the fins off of the smaller ones). These are so new that I don't have a real feel as yet for what they will do with various fish. I can tell you that they are very active, and never seem to stop moving, especially when I approach the tank, and they think they are going to get more food....little piggies!!! LOL.
They love to jump out of aquariums, so if you get some COVER THE TOP!
The fish are selling on the on-line fish stores for $24.99 each (plus shipping cost). If you can buy them at a better price at the store you mentioned (you don't have to pay shipping), get them. They rival the Electric Blue German Rams in color, don't they? They are very pretty fish.
After looking at the fish that I have (80 or so left, after selling a few on AquaBid and locally), I believe I can tell the difference in the males and females on some of the larger ones. The larger of the fish appear to be mostly males, with very sharply pointed fins. The females seem to be shorter bodied, with rounded tips on their fins. We shall see. Also, what appear to be males like to display for each other, much the way male Bettas do. Let me know if you get some. And remember to cover your tank if you do!