It's not actually a flugabone, though sometimes people sell them labeled as one.
What it really is is a fiscorn, a type of bass flugelhorn in C used especially in Catalonia. Cool instruments. But I've only read bad things about the Berkeley one, so I'd be wary. Apparently they don't play anywhere close to in tune. I wouldn't pay more than around $200 for one personally, and only as a curiosity at that.
Here's a pair of fiscorns in their native habitat, in Catalonia:
https://youtu.be/_ewew6dkvnA?si=SS7mT2hRBQwcFhz4