Well, my female is really sweet(she loves her "Tank-brothers" the Platies). It really depends on the betta. If you buy some, I would suggest floating them for a good long while, just to see your bettas reaction. Mine kept staring at them :). And while buying them, try to get the most clear looking ones. If they are all cloudy, then wait a little while for a new shipment.
In my experience, most bettas will end up eating the ghost shrimp anyways. I had one girl who lived with them for weeks and then suddenly ate them. LOL I got them for 10 cents a piece, so no big deal. They are really cool to watch though!