Oh please god no! There are browser plugins for people that like these sorts of things. I don’t understand the use case since you can barely read what pops up anyway.
This just makes the place look messy like on eof those pointless hardware review websites that nobody reads anymore because they are such a niusance.
The problem is that this is a bother for anybody that hasn’t come to the site before and who won’t realise they can opt out because they won’t come to the forums. They’ll just turn and leave and never come back.
It gives entirely the wrong impression.
If you need advertising to aid in funding, just use google adsense and say something nice somewhere like “Thank you for visiting this ad. sponsored site. Your clicks can save the world. Please also consider donating“