I've gotten the free containers and like them. But there are draw-backs. I would get them from the local grocery - both the bakery and deli sections. I had to go in early to fit their routine, and sometimes they wouldnt' have them. When they did, it was only 2 or 3, and I usually had to wash the gunky stuff from them. And the ones I got were more like 3 gallon size.
They are a valuable resource however - they are especially useful as food-grade buckets for washing produce outside, and then watering the garden. :)