I just bought the Red Sea C-Skim 1800 a little over two weeks ago. I posted a review. I will find the link and post it here. So far the biggest advantage seems to be that it is not affected by water level because it was designed for use ourside or inside sump.
But i only ahd for a little over two weeks, so I cant speak on the long term quality. it is a second generation, maybe third? (c-skim 1200 was the precious model).