I've used one a fair bit. A local buddy has one. I love it.
I'd take one over any similar sized utility hammer, and a few bigger ones. Low air consumption, hits very hard, highly tune-able.
With a decent sized press, and a 75lb Ironkiss, you'll be able to make bigger damascus billets than you'll likely want to handle.
In all fairness, I haven't tried the KZ hammers or even seen one in person. They do look very nice.