Hi! Author of Safe here.
This is explained here: http://www.getsafe.org/about#howissafedifferentfromtruecrypt. Here is a quick summary:
1. You can use your existing EncFS encrypted data on Mac/Windows.
2. 1:1 File encryption is much faster on network storage you don't control, like NFS, SMB, Drobo, Space Monkey, Dropbox, Google Drive. Most of their drivers/protocols are file-based. TrueCrypt is block-based, i.e. all data is stored as a single potentially giant file. This affects the performance of algorithms focused on caching and deduplication.
3. I designed Safe to be much easier than TrueCrypt to use. Try making a new encrypted disk with TrueCrypt, then do the same process with Safe and you'll see what I mean. TrueCrypt is very intimidating to set up for people who don't intimately understand how cryptography works. Safe just chooses the most secure defaults.
As for your second concern about caching. I can guarantee that no data is cached to the local disk unencrypted when using Safe. Don't just take my word for it, verify yourself. See http://www.getsafe.org/about#system_changes_more_info
Safe is not a competitor to TrueCrypt. They are different tools for different situations. I use both depending on the nature of the data I'm keeping private. Safe is another tool in this ecosystem and the main goal is to help more people take control of how their data is stored and transmitted and hopefully bootstrap mainstream digital privacy awareness.