Seems to me that private owners who know the ins and outs of their own engine would benefit a lot from an APS education but commercial pilots in and out of different machines on a daily basis would be hanging themselves out to dry by not heeding the OEM procedures, without knowing they were operating "Conforming Engines".
I have done the APS course, and i own and operate a lot of aircraft that have no mixture control at all, and those that arnt rotax powered, are aircraft with only 1 CHT and 1 EGT probe,
a relatively small percentage of the course focuses on EGT and LOP ops, the rest is how you can interpret that data you can get from those indicators, and understand the causes, and reasons behind those readings, and how to understand just what is happening with that engine. sure, do your runups and mag checks at low power before a flight, but what can you learn from that? sure, you can determine a dead Mag, but thats about it, after the course, you will learn just how much more info you can find out, and why doing a mag check at top of descent will reveal a lot more than just "A dead mag" you will know how to identify a failing plug, which cylinder its in, and upper or lower plug, so it can be changed before it fails..
a good analogy would by your ab initio training, the LOP ops will be the straight and level component only, but the whole course is similar to your complete PPL training, its not just LOP, its all about engine management and understanding what the engine is telling you..
how many pilots have been to different schools to learn different skills? or have just been to the one school only?
i went to another school to do Aerobatics, Advanced aircraft control and formation, i learned a lot of stuff, and had to UN-learn a lot of incorrect stuff, same with the engine course, i thought, operating an engine with no mixture, i knew all there was about it, and again, i had to unlearn a lot of obviously false info, and relearn from hard data, and also learnt a lot more about engines in general..