Oh Professor, I am right behind you....we just moved back from 3 years living in Budapest. Unicum is as good as it gets! I'd compare it to Jagermeister without the sickly sweetness, and a lot more herbal flavor. Still going strong in Europe, in both original and the far inferior "Unicum Next" (which I venture is the sweeter, watered down version you are finding). Sadly, I'm guessing you'll have to get Unicum duty free on the way back from Hungary if you want the real deal!
De semmi gond, tanar ur...egesegedre!
We've been making something similar for years as well. But Carr's Table Water Crackers have turned out to be the perfect vehicle, we substitute shallots for the red onion, and we'll hit it at the end with a large-crystal sea salt (Slovenian lately). And it's true - always the first to go at a party.
Another variation on the same theme is smoked trout, horseradish, thick sour cream, and chives, on the same crackers. Gotta have something with punch!