I am setting up yet another tank, and it shouldn't exceed 15L as it's really just going to be used for breeding/hospital tank. I imagine most of you have this scenario, so it this a good buy for 6.81?
You could also try putting a small piee of foam or filter wool in the nozzle. Pull the nozzle off and put it in the tube shaped bit. The shape of it holds the foam in place. This worked for my betta tank.
If you're using it for a breeding tank, the foot of a pair of tights (or a knee high) over the intake slots will stop any fry being sucked in.