Little late to the conversation but if you take care of your machine they will last over 10 years. It's like a car, if you don't do regular oil changes, cleaning, changing out needles regularly etc... you are shortening the life of the machine. I bought a used Melco back in 2003 and still plugging away -knock on wood. With that being said, I bought something in my price range, something I had the most experience with so I could do repairs myself and any troubleshooting on my own. I saw how much my old boss used to spend to have a repairman come out to fix something and I didn't 1. rely on someone else and 2. spend a pretty penny on their travel, hotel and labor costs. Trust me, I have seen multiple customers make it work with a single head. It made sense because they used it for "emergency" situations when their production company was flooded with orders and also to run sewouts or small orders. You would be suprised how many small orders they do and the largers one now they send out.
If you have a good deal I wouldn't pass it up because being able to do things in house when your competition can't puts you a step ahead of the others. Also, you might beat out timing on someones rush order because you don't have to wait for someone else to do it. If you can put some time and energy into your machine you will get your costs back but too often I hear of people purchasing and putting it to the side. It really is a different beast than screen printing.