I have used the Park Chain Scrubber for many years with my rear wheel on the bike. I would occasionally bump the plastic scrubber on the spokes. With the dummy hub you can remove the rear tire and use the scrubber without having to balance it and be mindful of the spokes. I wish I had purchased this long ago.
Typical excellent quality Park tool. This is one of those Why didn't I get this tool sooner? kind of things - makes bike maintenance chores SO MUCH EASIER.
Awesome tool to keep your chain from sitting on your chain stay when your wheel is off. Also allows you to spin the chain, clean the chain and operate your shifters when your rear wheel is off