Dahons, including new ones, do have some proprietary parts.
I assume you're looking at the Curve D3? If that's the case, I think the main proprietary part is the handlepost. That component tends to be flimsy -- as in, don't pull back on the handlebars or you are likely to eventually cause a failure. Anyway, if that part breaks 3-4 years from now, it may well be fleabay time for you....