Both Freesat and Free To Air receivers essentially do the same thing - offering 'subscription free' Satellite TV. The difference is that Freesat offers an on-screen TV guide that is easy to use via the remote control and enables you to quickly find the TV channel you want to watch, whenever you want.
Freesat offers a variety of channels (200+) to keep you entertained whilst Free to Air receivers offer all the freesat channels and many more but without the Freesat EPG (Electronic Program Guide).
Other benefits with Humax Freesat receivers are the recording capabilities as well as catchup TV and TV-on demand connectivity.