google adwords

I have a couple of codes for advertising on Bing Advertising and Google Adwords for free credits. Are the credits really free or is there some catch that you will have to pay for them at some point for some reason?

Whenever I have used paid advertising these are the two that I have used the most. Out of them I have always had better success with Bing Ads as far as return on the money I spent on the ads. This is in part because I was able to get more clicks for my money because Bing Ads is cheaper than...