edit: I may very well give it a try on that basis. I've got a large collection in Zotero on one of my machines, and a partially overlapping large collection in the Zotero app on my phone, and they are partially overlapping precisely because Zotero sucks at sync. It'd scratch a years-long itch to have my collection unified and easily available for both use and new accession, and Jendeley looks like it may well make that comfortably achievable.
I'm a hobbyist student of hymenopterology, not a professional researcher; this is an interest that needs to fit into a life with many competing concerns, rather than the work my professional life is built around. It should not be a great surprise when tools built for and by professional researchers fail to meet my needs - to say nothing of those tools being built to a typical academic standard of software quality, something in the implication of whose existence I am being quite generous.
I don't yet know whether Jendeley is any better, but it could hardly be any worse, and having been built with modern tooling and in a modern HCI paradigm offers significant promise of justifying my time and interest. (And as I do find things about it I don't like, it won't require software archaeology to fix them!)
Although there are many applications to organize documents, almost all of them are for only researchers. At least, all of them are not for me.
When you are tired of Zotero, please try jendeley. I'm waiting for you while improving jendeley.