Frank,
I use the SD all the time for carpet. It is a great little tool but it is like any other extractor, one needs to follow the standards of cleaning: Dry Soil removal; soil suspension and then extraction. When this is done correctly the SD is a great tool for flushing out the suspended soils.
I used TM's for 25 plus years and have no problem with them but they too are a tool for flushing out the carpet after proper soil suspension.
I use the SD now because of the type of homes I am in. It works well for my circumstances.
SA