Saving Star?

I am wondering if any of you use or have heard reports of using Saving Star? I have heard of it, but never branched into this digital means of savings. I signed up because I got 50 Swagbucks points to do so (getting me closer to more Amazon money, hence free diapers) So, from what I understand, after signing up, I choose the participating stores in my area, enter the store's card number (like my Kroger Card) and then load coupons onto the store card. The site also said after I save $5 in coupons through Saving Star, I get a $5 Amazon card as well-BONUS! So, I am wondering if anyone has experience with Saving Star? Are coupons ever doubled? Can store coupons be paired with Saving Star coupons? If you have some helpful insight I sure would appreciate it! I am bummed that Publix does not participate, but maybe this is an opportunity to tap into more savings elsewhere.