Yes, the G-Dec was replaced by the new Mustang series, but from what I can tell, a small step backwards in capability came with it. The G-Dec series was almost too far of a step for the traditionalists to accept - it looked to digital and they actually had the audacity to use the word 'digital' in the name. I think that was a big part of the lack of success of that amp series.

For example, the G-DEC 30 used a 2 speaker (mid & low driver, tweeter) system which is needed for amp simulation and the built-in audio playback/practice capability. The similarly priced Mustang (the 40W version - is a 1x12")

G-DEC allowed you to flash the brain so that you could turn it into one of 3 or 4 different collections of amp simulations. The base G-DEC had lots of metal amp sims, not needed by my father in law, so we re-flashed it to be the blues model.

Like Mac stated above, get one with a headphone jack and the ability to turn off the cabinet - that will keep the peace better than any volume coming from the cabinet - that much is sure.