Not familiar with a 1590xp, so I can't advise you on that.
Are you very mechanically inclined? Used chippers come with a host of technical difficulties for the inexperienced, and dealers are not inclined to educate you for free.
Beware buying any discontinued used models: that's how I got started. Not surprisingly, they are often cheaper than you expect them to be, until you discover the hard part of the deal.
Avoid drum chippers without a hydraulic feed. They work just fine, but they beat the crew to exhaustion feeding them.
You can usually buy a new chipper for much better financing terms (length of loan, interest rate) than on a used unit. If it breaks, and you are already poor from your payments, nothing beats having a dealer to do a warranty repair.
If you are in the business for real, but still kind of small, buy the smallest chipper you can find that will be able to handle the biggest job you expect to do on a regular basis. Don't waste your time on any small capacity chippers (6"-9"), unless you are going to haul it with a pickup and only trim small trees.