I got several and, they grew big enough to split. Since adding, I have had several good things happen: 1) Keep nitrate level down. 2)Become a biological agent, 3) Fry love them to suck up the infusia. 4)They grow to a point where you can split them and add to other tanks.
I do suggest a small heater. I have small ones that, I believe are petco's own. Tank stays at 78 degrees, always. In breeding tanks, I have adjustables so I keep it it above 80 degrees.
Also, if you are looking to get more bargains, buy them off of Etsy or Ebay. Much cheaper and much bigger than the pet stores.