I have a SA-250 with the fowler arc force kit in it. I do like it and it does make a difference in the arc however, its one more knob that you have to fool with. It is a 1 thru 5 tab and I haven't taken it off of 3 (basically neutral) in a couple hundred hours or so. It was cool and fun until I got it all figured out, now I just leave it on 3. If you was to flip-flop from puddle capping 24'' .500 wall to beading 3'' .188 it would be worth its weight in gold. I think the arc force kit would improve a sa-250 or 300D but, as far as a dc excited machines I would leave mine alone.

As far as the 7 range I personally don't know but, I have yet to hear someone say anything bad about it.