Provided its after everything as the water is returned to the pond that may just work.
As you have read they are actually different forms of a carbon filter but get muck in them I've an idea they may block very quickly, did you note the little red knobs along the top ?
Those are for gassing off air when you start running water through them.
I would also bring it in during the winter month because they do freeze if left out .
Your next problem would be sourcing them in the US but I'm sure they must use them in the koi world so a little bit of internet surfing may be involved so happy hunting.......
rgrds
Dave