ive seen this before but never fixed it.
but have fixed plenty of the porcelain slips/fingers that interlock.
i would say these will be easier.
first you dont have to grout them.
dont have to worry about lips because that part of the feature.
secondly with the porcelain that are on interlocking sheets you have to pin them up to stop them slumping down .
in your case looks like you only have lay on top of each other.
probably worth using grey in case you get adhesive squeezing out, and less obvoius if bits of gey get stuck in tight joints.
the one problem i do think you should be careful of is if you are asked to seal. there will always be a danger of sealer running down face and leaving marks.
you could using someting like stainstop in a bottle and spray on but make sure you wear a mask.
stainstop will be more user friendly than say hg impregnator or slate seal which are thicker and more dificult to use without run marks on a face like that.
regarding how to set out courses, ithink i would stagger each course randomly otherwise you get this repeat step effect.
i will see if i can post a couple of pics in aminute of how i set out two feature walls in slips at random stagger.
and maybe can fins one where asked to lay in line underneath which didnt look so good.