Filter cartridges can usually be returned to Coop and Migros supermarkets: => https://www.coop.ch/content/dam/act/themen/Publikationen/Coop_Infografik_Recycling_D.pdf => https://generation-m.migros.ch/de/nachhaltig-leben/recycling-guide.html#wasserfilterkartuschen

This product is often bought together with the Oskar Big, but it is not officially a matching accessory, we regret the confusion and inconvenience caused.

According to the Stadlerform website, the anti-lime cartridge also fits the Robert model. See here: https://www.stadlerform.com/de-ch/produkte/luftwaescher/robert/accessories/

We have bought this for Eva. To be honest I do not know if it is suitable for the others.

Yes it is!

Yes, has worked very well and fits exactly!