Skim Coat and Patch product vs Thinset for flattening floor prior to Ditra? - Tile Advice

[TileGuy45]

I'm preparing this floor for tile. I had screwed down an extra layer of 5/8 plywood but have left it off near the edge of the room because it jumps about 1/2" in elevation near the perimeter. I've filled in most of this gap now with a patching compound (Custom Skim Coat and Patch.) Now I just need to add a small amount (1/8" to 3/8" to make it completely inline with the floor beside it and smooth. I'm wondering if I should use Schluter AllSet instead of the Custom Skim Coat and Patch because it might be a little easier to work with. I'm not in a rush. What do you think?