Is it better to sync files in the mounted volume when they are unlocked? Would this allow bidirectional sync to take place?
Ah, I forgot about this option. Yes, you can do a bi-directional sync on the unlocked folder contents (I've edited my previous reply to reflect this).
This will probably be slower though, because the operating system has to encrypt and decrypt the data as it's being copied.
Does dropbox handle things better?
Dropbox does not handle things better, but you can use it,
just follow these instructions.What does the folder Temp in Data contain? It is present on one computer but not the other
Nothing of value, you can ignore it. It's just used by Espionage during initial folder encryption to host temporary folder mountpoints. It doesn't actually contain any data.