Still tile it regularly for builders. Know which adhesives work and which ones don't so don't mind tiling it. Usually spec backer board for my own jobs though.
I've ditched plywood all together now , unless am overboarding it with backer boards ! Builders in our we country love it ESP on shower walls, if I have to use it then it's a rubber crumb , 2 part adhesive !
I don't see the reason for using marine ply!?! What's wrong with strengthening the wall with stud work? Not entirely sure why they haven't tanked the whole shower area either!?!
as for whether the job is any good... Only time will tell. I wouldn't call it good tiling method. I wonder if they used a 2 part addy, or rubbed gear... Lol
Tiling to ply or timber in general should be avoided where ever possible if you are tiling to a timber substrate please refer to BS 5385 Parts 1 & 3. The TTA are currently revising a technical document which refers to tiling to boards and sheets which will include timber and backerboards. Bob Howard MBE