tefl is good. I did it as a career for 10 years, with a Dip and Masters on the way, and ended up in teacher training (still do some TT part time). It's one of those things you can do for a few months for a bit of sunshine, money and experience, or stay at it longer and get some quite good jobs.
It's good experience though, especially as more and more UK Uni students are from overseas. Showing you have experience of teaching non-native speakers is a good thing.