Dave86,
If the bees have the ability to get natural pollen they will usually not have much interest in a pollen sub.
I dont use feed bee, I use Ultra Bee, but the results should be the same. In early spring when they are DESPERATE for anything, you will even find them taking grain dust and sawdust back to the hive... feed them the pollen sub then and they will take it like crazy. As stated, once the natural becomes available you will find they are not as interested. Keep it handy for when they need it.