Some offers work, although not all of them. I've had a few "dead" offers that have never credited me.

What I would suggest is to just do the free offers, so if they don't credit you are not out of pocket. The offers where you have to pay for a service I would avoid.

The only ones where you have to pay that I have ever done is the betting ones - simply because I bet online so opening new accounts when the World Cup was on was of benefit to me. I created 3 online accounts, got paid out the tokens on two of them within an hour or so - but the third one took 3 weeks and multiple emails to "support" before they finally credited me - and I think I only got the credits as I screenshot EVERYTHING so could give them proof of every step.