Jax:
A little history is in order.
The original AN/DP course was designed to introduce student to modest decompression (one deco gas etc, etc). Extended Range was originally intended to build on those modest limits AND allow for tougher conditions, including longer decompressions with two staged gases. Depth was always a secondary factor.
However, Extended Range became a course used to allow divers to get deeper without the use of helium to temper oxygen and nitrogen toxicity. As such, only a few of the instructors I know diving in colder water, taught the course, since it was easier to teach the newly released Entry-level Trimix, which was essentially the same skill set. (Now all this was in the 1990s).
Several TDI instructors -- me included -- adapted Extended Range to become a sort of expedition diver class and forewent the deep on air aspect... FYI, the outline I developed for my old extended range course is the framework for a new course and book I am working on specifically for expedition and support team divers.
As time went on, TDI developed Helitrox Decompression (which I teach in replacement of AN/DP) and Extended Range became a sort of red-headed step-child in a large area of North America. The last instructor program I taught at this level was someplace warm and far away.
Would you get anything from the course? Depends on the instructor I guess. Personally, I believe you would do better to do a trimix class or get a Helitrox Deco upgrade, which would allow you to dive to 60 metres and 45 metres with an equivalent air depth of 30 metres or less.
:laughing: 
:joke:
