Worth the risk I think. Looks like these odds were created based on the names of the teams only
Holland have been horrendous lately while Wales have been pretty solid. They last played each other in another friendly in June 2014, which Holland won 2-0 at home. But this was the same month they went on to finish 3rd in the World Cup. Look how far they've dropped since then, not even qualifying for the 2016 Euros. Wales have only lost one game in the qualifiers (away to Bosnia) and even beat the #1 ranked Belgium (although that ranking is a joke, Belgium are nowhere near being the best in the World, or even Europe)
Will Wales win? Maybe not, but I think odds of 3/1 are pretty good if you want a gamble. And keep in mind British teams never give up and usually treat every game like it's a World Cup final. Holland probably don't give a shit.