I used to have the 22-580 which was a 2 blade machine with 2 speeds.
The 22-590 is 3 blades with 2 speeds. It looked to me like a re-engineered design to cut costs. A lot of metal was removed.
The blades appear to be available. Tools Plus for example shows them to be in stock.
http://www.tools-plus.com/delta-22-591.html
Look like the narrower knives like my DeWalt 735.
If the CL post is going for $100 and it is working, it may be worth considering. I had my 22-580 for several years, passed onto another forum member last Oct, who is still using it as far as I know.