I send students TDI e-Learning for: Cavern, Cave, Advanced Nitrox, & Decompression procedures as needed. I don't think they suck, but they certainly are not top notch or anywhere near what they could be. Many NSS-CDS instructors use this e-Learning even though we teach to CDS standards and not TDI.
What these do accomplish is it allows the student to immediately begin learning the topic without having to wait on a book to be mailed to them. It allows me to be able to cut down on face-to-face classroom time with the basic basics and to be able to more thoroughly explain the finer points, and details of the topics. The e-Learning has a written exam included which is also a time saver. Learning does not suffer; it is simply streamlined.
Some argue that e-Learning detracts from facetime with students in an academic/classroom setting. I agree with this *IF* the instructor relies 100% on the e-Learning to complete the academics. *IF* the e-Learning is used as a launching platform for learning with instructors supplementing what was learned online, in the classroom I find these materials worthwhile.
As an aside we at the NSS-CDS are working on, and 90% finished with an e-Learning module for cavern and cave diving! Stay tuned.