I just switched from DT's to Phytofeast myself. It is definately more cost effective to use and the shelf life is about the same. So far everyone seems happy with it. I mostly feed it to my tank for my clams and I have also heard that it is good for pods and I have gazillions of them so something is working.
Realize that the true "shelf life" of any photosynthetic microorganism is about the length of a day. Products that claim weeks or even months of shelf-life should be held in question. A microorganism needs certain amount of inputs: nutrients, light, water volume, that need to be provided within a fourty-eight hour span just like any other shipped organism.