Haven't used any of those myself. If you want to know if they are worth spending your time on; add a few good offers and a bit.ly link to your website. This way you can see how much traffic these sites have, and if you get any sales.
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it's depend on Boards traffic if they have good unique traffic then i think it's not bad for getting some traffic but i have no experience about this because its important question why that type of boards giving free advertising offer?
This is very simple way to know about that website is useful or not useful. Open your Google analytic account and check referring sites visit. Follow this way.
Although I agree with Jashlee about measuring results, I also need to raise my finger an state something. It is not just a matter of placing ads. The ads must be good ads to get clicks.
I have never heard about it so I don't think they are of any use. Most sites of these kinds are so full of advertising that it seems like spamming.
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