The Firm Feel rear bar is a copy of the original style bar right down to its mounting points, attachment method, and diameter, .75.
The bigger .95 or 1 Addco bars are actually very close in applied rate to the frame hung bars because of the longer pivot arms and narrower mounting points.
The adjustability of the Hotchkis bar is a huge deal to someone who wants to reallly dial in the feel of their car without getting in to any fabrication of end link locations and attachemnt points.