You can tell if its a new amp by seeing the letter:
LJ........numbers after that.
As for it being reliable....it's unknown at this point. It's still too early to tell. IMO, I wouldn't buy another MFW again until a year has pass just to make sure everything is ok again. Its a couple of months since I had the new amp in my MFW but can't say how long it'll hold up.
Just remember that AV123's warranties are not transferable, so if you run into issues, the original owner will have to do the leg work to get the items fix.