Hi,
I upgraded from 17 and I am very satisfied. I don't know if you need to upgrade from 21. Call Bobcad and ask them what you are getting that's different from your version.
I went to the training seminar when they were here in Chicago and I also bought the new training disks. You can beat up the Bobcad sales people if you drive a hard bargain.
I bought my Mach 3 program from Lee at Brianna. He was the cheapest.
Good Luck
Rick Geschrey