I now have over 8k miles on them. They were installed with stock springs.
They markedly flatten cornering attitudes. Ride is not materially stiffened.
They are a very high quality item. There is no rubbing or rattles whatsoever. Installation might be done at home, but not by me. I am 65 and overweight, so I can't quite do what I used to do with impunity. Clearance to the stock exhaust system is very tight.
Some people have commented that the Eibachs are only 1 mm thicker. Fronts from stock 27 mm to 28mm, and rears from stock 21 mm to 22 mm. Bar diameter is not the whole story. The Eibachs get much of their stiffness from being shorter than the stock bars and from using poly bushings instead of rubber bushings. The front Eibach is about two inches shorter and the rear is about six inches shorter - very approximate measurements.
One of the benefits of rear anti-sway bars on an IR suspension is that it tends to make the suspension act somewhat like a solid axel. This may be an attractive feature for drag racers. There is still wheel hop, even with bars and Cadillac's bushings.