I had a look at the eBay offer. It shows the insert installed and uninstalled but not a lot of detail.
I have a Hornady powder dispenser. I'm intrigued by what such an insert might do for it too. I never liked the way the factory tube works so I had planned to make my own adapter using my lathe anyway. But why not build on something that already works better. Can you comment on how well it works and how you might improve it?