Personally I would not buy used gear and will never recommend one to do so, but that’s just me.
What are you getting it for? and the OEM back is junk anyway even if the suit came with one, unless they are CE2 and is a full length back.
Personally I wouldn’t call it junk just because the fact that the it was on sale. Obviously I do not have that suit and have no experience crashing wearing it. I guess it all depends on your application. A $1500 suit when compare to $3000 suit is probably junk too.
I say just spend as much as you feel comfortable, cause I do believe in spending as much as you can on gear to minimize your risk of injury, IF you have an accident; even though I personally wore a $299 cheap suit myself…:rofl