Hartz ultraguard pro for cats, Does it work?

I got this product at wall-mart last night and treated my cat with it. She goes outside quite often. About a month ago my husband spread tick granduals on the yard and this helped alot keeping the ticks off the cat and the kids. I got this product just to give an extra boost for the tick and flea protection. She is a great mouser but I was afraid of her getting parasites from mice and birds she kills outside, so I put a collar with a bell on it around her neck. I don't want to keep her in the house all the time. She refuses to use a litter box unless it is raining or super-cold outside. She goes outside like a dog would. Fine with me, keeps the house from smelling. My question is does this product (hartz ultragaurd pro for cats) work well? Is there something better? I don't want to keep her prisoner inside the house, but I want to be as safe as I can be letting her out.