The hand pumps (at least the Benjamin and Hill) should have gauges. You can fill to 2500 or 2800 PSI on the pump gauge and learn how many shots it takes before dropping below the reg pressure.
Those regs are also adjustable. His is set at 1400, but you can set at a variety of pressures.
The problem I have with regulators, especially the aftermarket regs, is that once set, that's it. If it's set to shoot a Crosman Premier 14.3 grain well, but you want to change to a JSB 18.1 grain, it just shoots the JSB slower. You have to disassemble the gun, and adjust the reg, put the reg back, air up the gun, try the new setting, and if it's not right, do it again. Way too much hassle.
The beauty of the Marauder is that you can adjust the gun with three hex wrenches. It has infinite adjustability between the hammer spring, hammer throw, and transfer port adjustments. You can do this at the range on the bench with minimum of hassle. Just keep a record of the settings and you are good. Once you know the settings for each pellet, it's a matter of a few turns of a wrench and you are ready to shoot.
So far, in my experience (for whatever that's worth), the JSB's shoot much better at longer ranges than the crosman's. The Crosman's are just fine at shorter ranges and less expensive to shoot.
With a pump, the number of shots per fill will be very important. You can usually figure about 30 shots per fill, and the reg won't change that much is my understanding. The last set-up I did on the Marauder had a std deviation of around 8 fps over 30 shots without a regulator. Still working on the tune, but with the gun's current set, I don't see the need for a regulator.
Again, once you put the reg in, the fun is just starting while you get it adjusted and shooting the way you want. Lots of trial and error, and adding too many variables makes shooting NO FUN AT ALL!
Personally, I think shooting the gun, getting to know the gun, then adjusting or deciding if you want a regulator is the way to go. for me, I've decided that for the Marauder, no regulator for me. As for you, that's your call. Good luck whatever you choose.