Does anyone believe in, or have positive experiencewith, the claims of
products that they include bacteria that eat up the thatch in a lawn (or
grass that you wish would become a lawn :-) and that you no longer need to
mechanically scarify?

There are two products available here in Belgium: DCM Microgazon and
Vilmorin VilmoGazon (gazon is Dutch for lawn).
Do they work?
--
Robert