TLA do something kind of similar. It's not totally free but it's a great deal anyway. New advertisers buying a start up kit get an extra $100 worth of links when they credit their account with only $25 - kind of 400% extra free if you like.
I tried bidvertiser's offer as an advertiser, and it sucked big time. My option: bidvertiser = useless
We have a new promo code. Use DP02 when depositing funds (Paypal, ePassporte, eBullion(ec)) 10% bonus credit for every $20 deposited
I also used the free $20 and I used it to target traffic to AdToll.com and it was almost a 100% bounce rate and had not one sign-up.
I guess all the providers give you some kind of incentive to join. You can use google adwords voucher to get $50 free, Yahoo will offer you coupon for $100 similary other providers match your deposit.
I don't find bidvertiser useless but would not advertise with them as you don't get the same bang for your buck as you do with other PPC (CPC) programs, anyways, most companies offer free incentives to join, for example 50 free in adwords for a $5 deposit. Before you invest in advertising always research the company and their user experiences. Even if they offer the best deal in the world, there may be someone better for you personally.
I did, got a bunch of clicks, absolutely no leads, no returning visitors, then charged my account for $180 after the initial 20 ran out.