> My main complain is that it has a rather limited built-in web based app to transfer from your laptop/PC/etc to the device directly via WiFi but not the other around.

You should take a look at Symcthing, that's what I use to keep directories in sync across devices securely. There's a slight learning curve, but once you grasp the concept of devices combined with folders and how they interact it's a breeze. You can set it and forget it and it will do it's magic.