Nano Skimmer

[Coderad]

I was looking at Tunze Nano Skimmer. Heard good things, but low levels of oxygen returened to the water.
What do you think?
Is there a better skimmer around that price range.$170
I have a 15gal nano with a 4gal sump. Sump is only 9 3/4" x 9 3/4", would prefer insump skimmer, cause tank is not drill and there is not much room with an overflow box.

Thank Cody