Don't have one but have seen them used. They are good for removing modifications made to the signal by a factory HU when the HU absolutely can not be replaced.
I ran into this problem with my sable. It is always possible to run a head unit, just run it to a wierd place not in the dash. The cleansweep, although theoretically a good idea, in the long run isn't an amazing product. It does all it can do, but is no where near as good as a headunit.