They aren't my cup of tea, but they are getting more and more use on a wide variety of cars.

I guess if you like the really low look when the car is parked (and who doesn't?) then they have some merit, but I like a car (van) looking low all the time on a good set of springs and shocks.

I've had no experience long-term with any, so I have no opinion on what trouble they may cause to other components. I'm sure there must be some people here that have had some experience with them.