I highly recommend applying a surface membrane when building showers. You can get away without it on walls if you use a moisture barrier of the studs, concrete backer and thin set mortar, but the problems occur from the curb down.
I like the Kerdi method because I give the client a watertight shower, not just a water resistant one. The secret is the Kerdi drain. Most failures I see start with improper waterproofing of the curb. If you use the old method and then fasten concrete backer over the curb, you have ruined the membrane cuz now it's full of holes. That is not the way to build a shower.