The Facile Princeps is a cool concept, and due to design rather strong. Even though the mechanism appears simple it was rather difficult to get everything timed correctly. Many guns were worked on by smiths who probably shouldn't have been doing so, thus creating issues. They had one flaw also that made them easy to damage by someone less careful. Value will come down to condition and if it functions as intended.
I'm rather fond of mine.
You're welcome to email me pictures if you'd like. I'll post them for you.
