Useable Energy Explained
It's difficult to directly compare the amount of work you can accomplish with a Power Tank vs a compressor. A compressor with an auxiliary air tank has a minimum and maximum pressure which tells the compressor when to turn on and refill the tank. Typically, a compressor turns on when the aux tank falls below 90 psi and turns off when it reaches 150 psi. So of the 150 psi stored in the tank, not all of it is useable as, below 90 psi, there is not enough energy to refill a tire or run an impact wrench.
CO2, on the other hand, stores its energy as dense liquid CO2 and CO2 vapor. As the CO2 vapor is used, the liquid boils off into vapor, giving you a constant and consistent head pressure of about 500-800 psi. Whether your Power Tank is full or nearly empty, you have a consistent head pressure until the CO2 runs out.
When comparing work performed, we use the metric of useable energy. A 10 lb Power Tank can perform the same amount of work, ie. has the same useable energy, as 400 gallons of compressed air at 150 psi. Or to put it another way, if you filled a 5 gallon air tank with your 150 psi compressor, then used the air, then filled it up, then used the air, and on and on, you would have to do that 80 times to equal one 10 lb Power Tank.
Another way to think about it is comparing a lead acid battery like in your vehicle with a lithium battery like the one in your smart phone. A lead acid battery is charged to about 14 volts and can be used down to about 11.5 volts. Below 11.5 volts, the battery is considered dead because it can no longer start your engine until it is recharged. On the other hand, a lithium battery can be charged to 100% and then used with no loss of performance until it is near 0% charge.