Well, it all depends. I know that refurbished isn't a used piece. It's a piece that failed testing and was fixed. And since it was fixed, it couldn't be sold as new. Call TheZeb and ask them what they mean. TheZeb is an awesome place.
I called TheZeb since I was also curious. Those amplifiers are in awesome shape. Either the amp initially had a problem on the assembly line and was fixed, or it was used, had a problem, and was fixed. All the amps that were sent to TheZeb are in excellent shape. The warranty isn't TheZeb's warranty, it's directly from HiFonics. I would say that those amps are worth it.