I think it depends a lot on the destination of travel - if it's a very specific masters needed for a very specific career, or if it's an "enrichment" type masters.
I did a masters straight after my degree because I was feeling disillusioned. My degree hadn't allowed much opportunity for picking own topics/diversification and forced me through a lot of modules that I passionately hated, and my confidence was at rock bottom, so a masters was an opportunity to see if I could fall in love with it and wanted to carry on with a career in it or not. It was however at the start of the recession when it was pretty hard to get a graduate job in the first place, and I got a scholarship which also meant it was a reasonably economically viable option for me to get some breathing space at the time. For me it was worth it, because it helped me work out what I actually wanted to do, and I managed to get the research I did published with a bit of tweaking, which I think has indirectly helped me, and would certainly help if I wanted to side-step into academia at a later date. However, part of me wishes that I had - either straight before or after - gone and done some travelling, and that this may have been quite beneficial for me in terms of personal development and confidence. However, in reality, I probably didn't really have the funds. However, once you get on the hamster wheel of working and having "responsibilities", that becomes much harder to do...
I think if I was advising 21yo me knowing what I know now, I would say apply with deferred entry, get a working holiday visa and go travelling for 9-10 months, apply for a load of graduate jobs just before you fly home, see if anything lands on your lap and if not take up the masters!