Have any of you used the various cold air gun coolant
systems and if you have, what are your opinions on the
products?

It depends on what you're going to use it for. I see a fellow said it works
great for plastics. Sounds right. I tried one for grinding endmills, almost
useless. There's just too much heat being generated compared to the ability
of the gun to carry it away. On occasion I use an air blast for cooling and
chip evacuation when milling deep pockets. Again, a cold air gun wouldn't
help much here.

Karl