If same as in my tank, they will quickly breed to nuisance status. Just wait awhile and you will have many, many more.
Since I introduced my sixline the snail population seems to have definitely gotten under control or at least stable. I frequently have to go on a "snail hunt" after lights go out as that is when they come out to feed on algae on glass. Not a bad thing, but not in the hundreds. I think Matt pointed out the fact that they must be using up lots of calcium creating those shells. I have hundreds upon hundreds of empty shells in planter next to tank.
I suspect the sixline must eat the eggs or very little ones.
Good Luck!