The important thing with a pump is that you have control! You can stop at the spot in the pressure curve your airgun likes. While, with a scuba tank, it's hard to stop at right the exact point because the pressure rises very fast.
Also, once a scuba tank or carbon fiber tank starts losing its pressure, you cannot put more into a gun than is available in the tank. But, if you don't feel the difference, there is no point in asking. Good question, good topic!