Does it fit under a De'Longhi Dedica or other home espresso machines?

Yes. At about 2.3 inches wide and 3.9 inches tall, it sits beside or under most home machines, including the Dedica line. It is too small for cafe volume.

How many pucks does it hold?

Roughly a handful of spent pucks before it needs emptying. That suits one or two drinks a day; heavy users will empty it daily.

Is the knock bar removable?

Yes. The bar lifts out so you can tip out the grounds and rinse the cup. The wooden base should be wiped, not soaked.

Can the wooden base get wet?

It should be kept dry. Wipe it with a damp cloth and dry it promptly; leaving it wet can stain or swell the wood.

Is it worth it over a plastic knock box?

If you want a compact, better-looking box with a quieter knock, yes. A basic plastic box does the same job for less if looks and materials don't matter.