They seems to be one of the leading companies but therefore they are picky to publishers as well. I've worked with them in the past and although they don't have too much ads for my site they have really good selection of advertisers to choose from. For some reason my account was blocked although I didn't break any policies and I didn't tried to re-establish relations with them after this.
Also the biggest drawback with using CJ especially on big sites with articles is that in times when I was using them you have to track each link to them, as advertisers keep to expire and once this happened people from the ad are redirected to error page, so you have manually to take care for removing or replacing each link.
But maybe now things have changed and they are replacing it with link to similar product...