Is Bidvertiser ads are effective? And can I get 20$ free for my ads without credit card details? Its importnant for me. Please help. Thx

You need to submit your CC info but it will not billed if you set $20 as a campaign limit. Effectiveness totally depends on your skills and offer. With $20 you actually does not gain much because Bidvertiser has quite high CPC, better is to get some Adwords coupons and try out Pay Per Call offers from Offermobi to get feet wet..