This is a low cost yet well-designed and durable knockbox, for anyone looking for a decent yet inexpensive option.
As with most espresso related accessories, you can spend just about as little or as much as you like on a knockbox. If you’re someone who just wants to invest what they need to for a tool that does the job, this is probably the one for you.
The rubber base means it doesn’t slide all over the place while you’re clobbering it with the portafilter, and it reduces the overall volume slightly too.
The rubber bar does quite a good job in that regard too, and it does sometimes come out of the holes and have to be put back in - but the same is true for most similarly priced options.