Basically I have a small web-app I've run a few years and recently decided to finish up some overdue features and 'release it' nationally.

I am considering putting ads on it to generate some minor passive income; really though the ads are meant to drive people to the pro (ad-free) version etc.

Since I don't expect the ads to generate much is it even worth it?

And given that it's likely to not make much off ads (possible the 'pro' account would make an ok passive income), what are the easiest/simplest/best options to put ads on a small web-app? Rolling my own is another option.

Any experience anyone has had with ad networks for small web-apps would be greatly appreciated, thanks !