What part do you not understand?
Ask yourself why are there separate courses for everything? How come I can go into dive shops and see individual prices for these courses?
Answer: Because TDI allows it.
Do not judge TDI based on your one instructor. There are some good ones, but there are some real big hacks too. So if all you know of a potential instructor is that he is TDI...well, that wouldn't count for anything in my books.
No need to get your panties all in a bunch. I seriously am interested in your opinion. BTW, I think the only folks I've heard actually judging another agency is you and the two guys from Ontario. All I'm saying is that my experience, and several others who have taken TDI courses, is that the courses are taught together. I didn't help develop them so I can't tell you why there are separate courses...you know what they say about making assumptions. I can tell you this...the Extended Range/Trimix manual is one in the same. It makes me wonder why anyone would teach the classes separately if there is one manual for the two topics together.
I do agree that a poor instructor can ruin a good course materials, but the same can be said for a good instructor being able supplement and improve on bad course design.