As far as reliability: I have never had a single issue with any Fractal product. I have owned AxeFX II, MFC101, AxeFX III, FC12, AX8, FM3, 2 EV-1 pedals, and 2 EV-2 pedals. I tour internationally with my gear, and while I carry a backup processor (Tech21 Fly Rig), I have never had to use it. My Fractal gear has been absolutely reliable under all conditions.
Should you buy used at the same price as new? Only if you need the FM9 versus what you already have. The wait list is long for this new unit, but if you really feel it's the right fit for you, and you can trust the seller (or purchase through something like Reverb where you can file a dispute in the even the unit is misrepresented / non functional), then you probably aren't taking much of a risk.
I don't get anything in return for saying this: I would buy Fractal products without hesitation. They are battle-worthy tools that let me express myself in new ways.