Sure you can use Terminal to purge but many people are not familiar with or comfortable using Terminal. I don't shy away from Terminal solutions but in this case, the app provides an MBI so I can see at a glance when things are getting tight, and I just click the MBI and the purge is done for me without having to access Terminal and type... So I'm a bit lazy that way.
Freeman works as advertised and it a handy out-of-the-way app that is useful for me several times during the day. It's well worth $2