I've been a heavy Standard Notes user for a couple years now, and the added function of Zettlr looks extremely appealing to me (images, linking, much nicer rendering, etc.). However, to really give this a test drive to see if it's a suitable replacement, I downloaded all my Standard Notes as plain text and tried importing them. This caused a ton of bugs/errors when trying to navigate and use the results. First, it complained about not being able to detect the file type -- again, these are all plain text that end in .txt... Second, it seems to have a ton of trouble with renaming folders: it works the first time, renames it on the filesystem, but then doesn't keep the change in the app? Then I try to reload and rename the folder back and now it throws null variable errors left and right? Then, I try to create sub-folders to start organizing the mess of notes I just imported and... big choke, can't create the folder, sometimes it gives an error and other times it just does nothing. The performance (speed opening tabs, scrolling notes) seems to degrade quite a bit with the number of notes I have.
So... this looks like something that could be really great! But there's a lot of friction still to having it get out of the way and let me be organized.
I am also a long-time SN user but I've never really liked the editor. So, I used a bit of free time to turn a C GTK SN client PoC into a somewhat proper Rust app (https://github.com/matze/iridium) and hope to put in more effort the next few weeks. You might like it if Linux is your platform.
Zettlr uses virtual folders basically so that your physical organization might not reflect how it's organized in Zettlr. Also, Zettlr is for markdown so you basically have to rename your files as plaintext files are not supported.
So... this looks like something that could be really great! But there's a lot of friction still to having it get out of the way and let me be organized.