The S17 power nozzle wil not work on the S20. The S20 has a direct connect hose with direct connect wands into a direct connect neck on the power nozzle. Although the S17 nozzle has the metal brushroll, I still prefer the S20 nozzle. It is easier to maneuver and has a wonderful roller inside. It also has a slow start motor which gives a longer motor life.
As far as the HEPA filtration on the S20, using the HEPA bags give the machine HEPA filtration. The Hoover type S bags are also work in the machine, but are not recommended.