Well I seem to be getting conflicting information on this shrimp. I was going to go with 2-3 Amano Shrimp. I asked the guy at my local fish shop about the shrimp he would recommend with a Betta. He pointed me in the direction of the Amano Shrimp as it is one of the bigger shrimp and my Betta would be less likely to try to nom nom or pick on him. He had them, but I'm still cycling.
So I went to Petco just to poke around really and asked to look at their Amano Shrimp just to see what he had in stock. Well he didn't have them, but he's supposedly the best "fish guy" they have there. He of course wanted to act like his usual know it all self and started digging at me about why I wanted it. I told him I was going to house 2-3 with a Betta and 6 Cory Habrosus in a planted 10 gallon tank.
He proceeds to paint these things as monsters. He's like yeah if you put those in a tank with those fish they will gang up on and attack each one until all the fish in the tank are dead. He told me I could have one by itself and it wouldn't do this because it wouldn't have a gang mentality. I'm floored at this point because one I thought these things were effectively algae cleaners and were more of a target for the fish to eat.