Used, no cracks, has a small chip 1/8" X 1/8" and a few tiny fleabites.
Mostly cleaned, has traces of mortar.
Can be set in thin-set too, but the cement-board needs to be cut out to minimum dimensions. (see below)
Use mortar, silicone quick set, or a waterproof fast setting adhesive / epoxy.
Keep it well supported, and taped to the wall during the setting process.
Outside dimensions roughly 6-5/8" X 4-7/8".