BoxCryptor already offers a great level of security by using AES-256 encryption which has been approved for top-secret information. Although this level of security is already very high without these "features", they increase it even more - mainly because they make it hard to modify the encrypted data.
No Filename initialization vector chaining
When filename initialization is enabled, you can copy an encrypted file from folder A to folder B and the filename is still decrypted properly. With this feature, this is not possible anymore.
No per-file initialization vectors
Right now, every file has the same deterministic initialization vectors. You can copy one block of an encrypted file at the same location in another encrypted file or tell if two encrypted files are identical.
No external IV chaining
With external IV chaining, the data in a file becomes tied to its filename. E.g. if you rename an encrypted file outside of EncFS, the data will no longer be decryptable.
No block MAC headers
With block MAC headers, it is possible to detect if an encrypted file has been modified outside of BoxCryptor.
No per-block random bytes
A special setting regarding the per-file initialization vectors.
You can find more detailed information in the EncFS man page (under "Filesystem options"):
So these "features" can increase the security, but even without them BoxCryptor offers great security for your private data. Decrypting your files without the correct key is impossible*. Of course, we always want to even increase this level of security and implementing these "features" is on our todo-list!
I hope I could answer your questions.
* It is important to know, that every encryption can be broken if you just have enough time and/or resources ("It is theoretically possible to break such a system but it is infeasible to do so by any practical means." Wikipedia).