Pneumatic pumps are very much a case of 'you get what you pay for'...
Rule 1: If possible always get a hand pump that offers a higher pressure range than what you actually need to produce. If you've ever tried to squeeze the last 10 kPa out of the range of a hand pump, you'll know why!
Rule 2: Buy some good quality hoses and fittings. No pump will keep up with leaks caused by poor hoses and fittings. The hoses you use for instrument connections just won't cut it. They have too much volume, and swell under pressure and ambient temperature.
Finally: Process fittings such as Swagelok and Gyrolok, while being great for fixed installations, were never intended for the continuous coupling and uncoupling associated with repeated calibration activities. The Ralston system features low bore, non-swell hoses with fittings that don't require any tools to get a bubble tight seal. Get yourself a Transtek Hose Kit and you'll never look back!
Hint: When using pumps watch out for the 'Adiabatic' effect. You might think the pump is leaking after you stop pumping. In fact this is just the volume adjusting due to all that heat you produced while pumping it!