Just a personal thing But I don't like the idea of applying SG after cleaning or even on new carpets unless the carpet can be left unused for at least 48 hours, which in most cases it cannot.
I did a Scotgard course run by 3M at Bracknell many years ago and became a SG licensed applicator.
They no longer operate this scheme.
For the SG to be properly applied the carpet is quite considerably wetted with the product, not something I want to do following cleaning, when you really want it dry as soon as possible. If the correct amount of product with the correct coverage is not applied (ie: just misted over) then it will not have the desired effect.
If anyone walks across the carpet whilst it is still damp with product they will 'track it off'.
If the carpet is not left neutral after cleaning, any alkalinity will destroy the fluorocarbon, making it pointless in applying it in the first case.
A bit like building a rod for your own back springs to mind.
Dave.