Are you on about Ready to Go? I've been going on there over 25 years and never had to pay and never had any issue with ads. It has 10 times the traffic our forum has mind.
You don't have to pay, that's the point, but you can pay for ads taking off and some minor extra features.
The ads on here are aggressive compared to any other forum I visit though, I've seen guns, child porn comics and all sorts. I wouldn't be comfortable posting here from a work machine! The rules say dont swear because lovely ladies lurk here nd get offended but the ads run wild
RTG is big, I guess because well ran and got in there early with well designed site and forum whereas FMTTM looked like cedar until about a year ago so playing catch up.