Hi Evgeniy-M,
Thats an interesting solution, Im surprised Shopify support havent suggested that to us as a possabliity but then their only solution for everything seems to be buy a paid app.
This would still be a much clunckier solution than the filter by tags as it means setting up a metafield for each possible tag which is quite labourious.
Im just testing this out and have added the metafield within settings and then applied it to a product however I cannot get it to show as an option within theme > navigation > filters
I set a true or false metafield.
Also is there anyway to alter these metafields on mass as they dont seem to appear on the bulk editor when I try that which again makes this a very time consuming solution.