I like Breville's simple knock-box - I would recommend it.
Positive Product Points
Solid construction to this knock-box.
Negative Product Points
It would be nice to easily remove whamming bar.
Whamming bar is rubber coated so it won't damage your filter basket lip with use (assuming you don't smash too hard). This is a two part product with a plastic bucket that holds pucks with the brushed steel outer body. Looks nice next to a similarly finished espresso machine (like Miss Silvia). The inside portion that holds pucks being easily removed means you can dispose of the pucks and spent coffee with little to no effort.
What else can you say about a knock-box? Honestly, not too much other then is it nice looking and functional - both of which Breville's knock-box has.
I bought this product at a local specialty retailer. No problems.