I've used the july/01 version, I think it's the latest. The lack of docs hindered me in two ways, first I wanted to know how to use the I/O (already answered here), also I don't know how to single step; and when I run animate it moves too quickly.
I tried using this lately for serious development but I keep getting errors with my labels; it will say phase matching error, the label changed between passes. To me, the label looked correct. So I resorted to hand coding absolute addresses but got tired of that workaround pretty quickly
Note: I tried entering code by pasting. I noticed that instructions would change to uppercase if I press enter in the real editor, so I pressed enter on all my lines in case that was "needed" for the program to process my lines.
Another bug, it seems I have to close the variables window between assembling, as the listing in that window won't change during an assemble, and somehow what's in the window is the correct version... in other words if you change a label, you must close the window and reassemble and open the window again.
But, otherwise it's a cool concept and the best I've seen of it's kind.
Since then I resorted to one of the many dos assemblers but that's a real pain - I write in notepad, save (yes to overwrite), type the assemble command in a dos window, copy and paste the object file in two other windows, load the program in my emulator, then run and debug it there - it would sure help to do it all in one environment, at least for the pure 6502 stuff, and the built in I/O is great cause I would spend the extra time writing some i/o routines into my code just to help with the testing.