Kerdiboard is high density, extruded polystyrene with a proprietary covering both front and back (not their standard sheet membrane). The foam itself is waterproof, the covering helps provide some stiffness and vapor retarder functionality. Given the nominal 16" OC stud wall, once covered with tile, it is quite robust.
Wediboard is a similar foam with a coating on front back that is not a sheet.
Seams on Kerdiboard are treated with Kerdiband and thinset. Wediboard requires a waterproof sealant (not cheap!), but has an advantage that you can flood test it in 15-minutes or so while the Kerdiboard, kerdiband, and thinset requires 24-hours to allow the mortar to cure.
Both utilize much fewer fasteners, cut easily with a sharp utility knife, are easy and light to carry, the dust isn't carcinogenic, and provide a waterproof enclosure versus a water resistant one. And, doesn't crack if you get a fastener too close to an edge, or the studs aren't all in alignment and it must bend too much like a cement board won't.
If you try it, you'll like it.