I’ve just sent a letter to the headteacher along those lines.
I’d like to see a policy from the school on this sort of advertising, especially if it’s paid. IMO anything they put in my kids bag to bring home is implicitly endorsed by the school.
The leaflet itself raises a number of concerns. Asks for a bunch of personal info with a want / don’t want further info check box. What happens to your personal info. No mention of what happens if you ask for more info. No mention whatsoever of cost. Lots of red text saying it’s very important to complete regardless of interest, and this is backed up by a note on the envelope attributed to “The Headteacher”.
If they are to do this sort of thing I think there should be a very clear covering letter. Costs should be made clear up front. Any benefits the school gets should be made clear. And preferably a selection of schemes should be included.