generally its a solid metal top mount (strut bering) doesnt flex and move at all inder stress so it makes the suspension much tighter (just like what poly bushings do for the lower parts) the ride will be rougher and you will feel a lot more but hey theres a price to everything
Somewhere on here. Airjockie made a rather comprehensive line-art drawing of them, and what they do in a strut. I did some searches, and I can't find it. You might wanna start by filtering his posts. I believe the word "beer" and "Fart were NOT mentioned in it.