Look, of course it's possible to put on with these, but that doesn't make it a good idea. Just like it's possible to put half an inch of finish on an unprepped wall. It isn't showing us anything.
The main reason not to put on with the plastic is that you'll just be following the undulations and imperfect shape of the wall, yeah it might end up shiney and filled but it wont be flat.
The best time to use them is when a flat surface has already been achieved, like on the last couple of trowels.
You might be just about able to get away with it in an old cottage.......