As basic as it may sound, do not pay more for a used unit of what it cost brand new with guaranty.
I saw someone on ebay pay $2550.00 dollars for a Quintum tenor ,old, no guaranty.
The same exact Tenor, from the factory,support and I year guaranty is being sold for $2900.00.
Not worth the savings.
On my personal opinion, if the price is not 40 to 50% off the price of a new one, it is not worth the risk.
Some people think diferent, of course.
All tenors are software upgradable, but that you will need to buy a service contract on your own with Quintum. It is not unreasonable expensive.Call Quintum directly. Still small enough that you could call without paying .
Unless you find a basement sale (hard to find, since there are not to many abandoned units anywhere), you will do best going for a new unit.
My humble opinion.