So I just got 4 small Tiger Nerites and I'm thinking I'd like to get a few more. I've had little luck finding snails locally. I found these on Amazon and am curious which one is the better deal. I like the variety in the 6 but I don't have any trap doors and wondering if they are a better variety to own. I don't want snails to take over and that is very appealing about the Nerites.