Haven't used 'em, but in looking over their advertiser directory it doesn't seem like they have too many advertisers and the majority of the ones that they do have are online shops that I've never heard of -- no national recognizable brands. They're counting several advertisers (Roar, RedHot, et al) in multiple categories to make it look like they have a lot of advertisers.
That may be ok if someone else can vouch for their service and conversions, but without further info, it's a red flag to me.