I think you're right, and those credits will be so diluted that you'll probably receive them very slowly (since every credit earned is also earned by three other people in your upline).
I'd think it depends on what you have to advertise on it, and whether the returns from that advertising are worth giving up your online real estate for no cash upfront.
What were you thinking of advertising on it?
I see in the TOS that you can't advertise advertising. The potential here would depend almost entirely on what else you want to sell, and what other sites join and display your ad.
I had to laugh at this: "Let's say your niche is dog training and your biggest competitor is spending lots of money on pay-per-click advertising. If your competitor is a member of our network, you could see YOUR SlideUpAd appear on their website - giving you the chance for even better conversions than your typical link exchange site!"
Wouldn't it be just as likely that an ad for a competitor would end up on
your site?
If you Google the owner's name, you'll see he has a great many similar programs. Personally, if I were sold on using something by this guy, I'd look for something structured a bit more logically.