We are just finishing a new shower remodel. We are on slab but had to pour new sections we jack hammered out because I re-oriented the shower stall and drain. The walls are floated traditionally, not cement board. However we did Red Guard the float before applying tile to walls and ceiling.
If speed is the need . . . The Kerdi pan seems like a good call because you get a perfect shape immediately ... no sloping of a dry mix floor. At $500 for the entire setup, it is competitive with prices I have seen for dry mix jobs.
Have fun with your project!