It's only free in some locales, and not yet across the entire nation. I don't consider these a rip off. It's down to personal preference. I have tried the 30 day trial to two of the agencies, and I'm currently on the privacy guard trial.
Having been a victim of identity theft (the cock eater was too dumb to get the cards approved though) I can say that this is a monumental pain in the ass. If you're able to catch it early it can be of help. FWIW I normally do not prescribe to a monitoring service, and I do check each year, but that's mainly because I'm cheap; if I didn't mind spending a bit more money I think a basic credit watch is worth it. It may be transunion that has it for something like $10/quarter, and that includes a report every three months plus they'll email you if anything changes.
I used to think nobody would try and fvck me over but then when I saw it a couple years back I actually wanted to commit bad things to the person. So, it really can happen to you :Q