When you do a search for Sheble on this forum, you will see a lot of statements that Sheble's is a place where you just "buy your ticket". This is probably true for all other ratings, but for CFI, you will probably still need to pass the checkride with the local FSDO although there is a chance you could get their DPE.
My observation from having gone there is that you don't really go there to learn how to be a CFI. What you are really paying for is the legally required minimum amount of ground and flight training, a spin endorsement, the sign off, and their "networking contacts" with the local FSDO to arrange the checkride for you within the 8 or so days they promise. Notice I said "8 or so". I would allocate at least 10 days, ideally 2 weeks. American Flyers, on the other hand, will give you a lot more hands-on teaching practice during their course.
Mabye my class was unusually lucky, but the ground school instructor we had gave a pretty good review. The CFIs are like any other place- some are there just to build time and a few are knowledgeable and actually care. Try and get as many flights as you can with the latter type.
One more thing- don't expect nice facilities, planes, or any sort of organization. It's the most ghetto facility I've ever seen. You need to be proactive with their dispatcher to make sure you get what you need. They are nice people and willing to help, but you have to remind them. If you expect everything to be neatly organized and handed to you at the snap of a finger, you will not be happy at Sheble's.
My local flight school owner actually recommended I go to Sheble's so not all flight schools dislike them.
More questions, I'd be happy to answer here or via PM.