I’ll be honest, at first I thought this was just a bit of a gimmick that reduced the cup size.
I have changed my mind though, because it is another one of those things that you never knew you needed until you have it.
Simply put, part of the collection cup is indented so that it creates a ‘window’ which allows you to see the bubbles in the neck of the skimmer.
Why do I think this is a great addition?
With all other skimmers, once the collection cup gets a bit dirty you can no longer see the action of the bubbles in the neck of the skimmer, nor can you see how dirty the neck of the skimmer has become.
With this unique viewing window your view of the neck is never obscured. This enables you to monitor the bubbles at their highest point and dial the skimmer in precisely for maximum benefit, even if the collection cup is crammed.