Just chiming in to say that I have mine on the out take of my canister, basically because of the way the tank is set up, it was easier to fit it on the out take. I haven't had any problems or not noticed a reduced flow. And it still gets dirty!
i run mine off a fountain pump instead of the cannister.
I prefer not to tinker with the filtration by adding this and that to it, instead a fountain pump can stick to the side of the glass and do just as nice a job without any burps or flow restrictions.
Both could be quite useful. Use the first when you need tips on your plant tank. Use the second when your frustration that those plants just won't pearl finally boils over.