I've tried this same rear lower tie bar on my 94 Mitsubishi Mirage. It made a big difference. The car felt like it drove straighter down the road, not so flimsy in the back...but then again the Mirage had a fully independent suspension, so yeah thats why it made a difference.
I too, thought about getting this from ebay. I would, however, prefer a fixed bar that wasn't adjustable. The cool thing with our Civic's are that that plastic rear cover under the car would block your view of the bar, so you wouldn't be able to visually locate it without taking off the plastic cover which makes the car more areodynamic.

In the end based on my previous experience with this rear lower tie bar I would probably buy it again.