Standard shock pumps typically go to around 300psi. This is fine for air can inflation, but for shock servicing, much higher pressures are needed to charge the IFP, particularly in [shocks that feature a lockout]- faqload.com/faqs/bicycle-components/suspension/monarch-rl-2015-rapid-recovery. Some of these shocks will need around 500psi in the IFP for the lockout and/or pedal platform to work properly.
The Rock Shox 600psi pump is a pretty basic affair. Its got a 600psi gauge and a small diameter piston with long stroke to make getting up to 600psi less of a chore. There's a small pressure relief button near the head and a swivel tube with a nice long engagement. That's pretty much it.
Being more of a "specialist" item, these high pressure shock pumps are bit more expensive that the normal 300psi versions. Expect to pay around the $50 mark.
For IFP inflation when servicing Rock Shox shocks you'll also need the IFP fill adapter.