If I was using an app from a chinese company that sync'd to servers in China, I'd be extremely suspicious about what is being sync'd and what isn't. Anyway, you say you understand the risks and the value/privacy of your data so that is fine.
The Linux conversation has been going on for years, there are lots of contributing factors, the size of the user base, the number of distros, the communities preference not to pay for software/services, etc. As a commercial organisation, I'm sure that Evernote (and lots of other mainstream commercial organisations) would jump at the opportunity for a new revenue stream. It does seem pretty clear given the unwillingness for the vast majority of software suppliers to provide a linux solution that this opportunity is not big enough to warrant the risk. If you select a minority OS, this is the risk you take.