Quite good material. It is indeed expensive, but it saves you time, and time is money. Just be careful, it should only be applied to porous materials, as stated in the technical datasheet: FAST-COVER is applied to porous surfaces such as render, plaster, gypsum board or other drywall structures, wood, etc. [...] Not recommended for use on glass, plastic or metal surfaces. If it comes into contact with materials that do not absorb moisture, it struggles to dry. I tested it on an electrical box and while the putty had tightened on the surface, inside it remained in the form it has in its box.

This particular putty resembles mousse. It is much easier to work with compared to regular putty, and because it is like foam, it can fill even large holes without the need for a mesh or any other material to fill them. It is more expensive, but it saves you time as it dries much faster than regular putty, and if you work the spatula well, you won't even need to sand it. I was told by Isomat that it withstands moisture better and doesn't sag even if you nail it after it has dried.