The gluing with a gun-tube material is a potential problem, as is the CD grade plywood with large voids both interior and exterior. The use of a CBU in that application will at least be better than a sheet membrane as regards the voids in the plywood, but it's still recommended against by the ceramic tile industry.
We can't guarantee failure any more than we can guarantee success, we can only tell you what the tile industry and product manufacturers recommend and where the smart money will be betting.
My opinion; worth price charged.