Fog / spray effects the respitory system as well as the eyes and skin burning, etc. When conditions are good for its' use it is much more effective than either the stream or the foam. In conditions where there is almost always wind moving...such as on the beach or on water, etc. the fog/spray can be difficult to apply accurately and can also blow back on you. Foam was first used widely in corrections environments to reduce contamination. (not a big issue either with OC). The great thing about foam is they invariably try to wipe it off and end up wiping it into the eyes.