I've installed hand throttles on both the manual transmission my TJ came with the automatic I converted to. For low-speed crawling, they can really help. I only have pics of them on my previous TJ so I don't have the B&M shifter in my present TJ.
Placing the hand throttle actually on the shifter makes it easier to precisely and steadily control the throttle using your fingertips since you can rest your hand on the shifter while on a bumpy trail. Mounting it on the dash instead would force you to hold your hand mid-air which would make it impossible to hold the throttle steady on a bumpy trail. Steady/precise throttle control can make the difference between breaking stuff and not breaking stuff.