Wouldn't hurt to put them in, but also remember this, they are filter feeders, feeding mainly off free floating algae etc (if i remember correctly) so if you have a green water problem, they would be very happy to slowly eat away at the problem, but if there isn't enough food for them they will die, and when they die and you pull them out the tank, they STINK REALLY BAD!!!
I had about 4 in one of my tanks, and after they died, i said never again... since at times you really don't know when they are dead unless you can see something that shouldn't be picking at them, picking at them...