What pressure are nitrogen tanks filled to? If its 2500 psi or lower, that won't be likely be very useful. Even a large scuba tank filled to 2900 psi isn't very efficient, as I try to fill my air gun to 2500 psi, and you can only do that so many times when you start out at 2900 psi. Now a higher pressure vessel, even if its much smaller, filled to say 4500 psi, would give a lot more fills.