I use CamBam running on the machine along side Mach 3 with no problems. CamBam impressed me enough to buy a second copy which also runs on the PC control of the big machine at work. The advantage of having both programs on the machine is quick changes and reposting to Mach 3. Forty free sessions before you buy, a fabulously helpful user forum and lots of scripts and plugins, plus a useable CAD functionality. What's not to love?
I've done plenty of G-code programming, life is too short not to use a CAM program today.