If you're curious (like I was) if anything else in the Haskell ecosystem is using this, this page lists packages that have dependencies on tls in Hackage (the Haskell package repository). There are 26 packages that depend on tls.

http://packdeps.haskellers.com/reverse/tls

Meanwhile, HsOpenSSL (Haskell bindings for OpenSSL) has 22 dependencies:

http://packdeps.haskellers.com/reverse/HsOpenSSL