The more parts, the more things that can break or otherwise malfunction.The complex design of the Eppelsheim is what makes it so great. It uses linkages and other type of mechanics I've never seen on any woodwind. Really making it work very good. It's really something to see to know. I wouldn't call it "overly complex". The advantage of avoiding the very long hinges is very good and the much smaller case is very helpful too.
I know the Eppie horns -- even the Eppelsheim-designed horns are good, according to anyone that's played them -- but think again of Leblanc: Le Rationnel, Semi-Rationnel and Leblanc System instruments: wonderful horns, but very difficult to repair. Leblanc also had bunches of other "improvements" in keywork design that, when they were in proper adjustment, worked great. Out of adjustment sometimes = unplayable, even if it was a doo-dad that did nothing more than hold a key open. This is also why I found it interesting that the few contra players here that have had the experience of playing a straight horn and "paperclip" say that the paperclip's a better horn.