Full-disk encryption is block-level encryption. If you're using TrueCrypt to encrypt anything, you're using block-level encryption. There is no functional difference between them. If you are not encrypting your entire disk, then block-level encryption is a bad idea because 1) it doesn't provide authentication, and 2) block-level encryption (using strategies like XTS) is not as strong as regular authenticated encryption using CBC and a MAC or whatever.
If you're not using TrueCrypt for full-disk or full-volume encryption, you'd be better off using basically anything else. There are plenty of cross-platform tools for doing that kind of thing.
Authentication is the biggest problem with sector-level crypto, but the other technical problem with encrypting sectors is that you don't get a place to store the metadata you'd need to randomize the encryption, and so you lose semantic security as well. If you squint at it the right way, XTS is the ECB mode of sector-level (wide-block) crypto schemes.
If you're not using TrueCrypt for full-disk or full-volume encryption, you'd be better off using basically anything else. There are plenty of cross-platform tools for doing that kind of thing.