It is sand and cement self leveling but the guy who lays it has a very good name and says the 500 gauge plastic won’t be a problem but if it was heavier it would be.
this is more information on it
. The screed arrives on-site pre-mixed and is pumped to the area rendered inaccessible to traditional screed methods. The product is levelled off to give a smooth levelled finish. Once installed the product is cured with and appropriate curing agent.