I can understand not wanting DM candidates to use certain specialty type equipment. Don't exactly want OW students trying to learn skills from someone in a FFM. But why not a BP/W? I agree that it teaches students diversity in other divers' kits and teaches them to look for certain things during buddy checks instead of just assuming their buddy's setup is exactly the same as their's. That could create problems in an emergency situation. Not only that, but it might show students other types of gear that could work better for them after they're certified and actually help shops sell MORE gear. Just my opinion though.
If I may add some perspective.
With OW students ( and I one centre I teach uses BP/W the other Jackets) I use gear that is similar to teh students. Yes three are differences (no cumberbund on my Jacket and longer than normal Alt hose) but none are obvious.
I don't' want to over whelm them by explaining my gear, when there's is still alien and new to them.
I will so little differences, perhaps the way I stow my SPG or how I clip off my Alt, but that's it. I want them to learn from me so teach teh skills in the way they need to perform them.
When we move to AoW or Con Ed, then I will introduce other gear. perhaps my BP/W or explain why my normal regs have 2 x 40" hoses with the Alt coming under my left shoulder.
When we get to rescue, I'll get them to master the skills first in a Jacket (even if they wear a BP/W) then we can move to showing or using a BP/W and I might even throw in my Side mount - just so they can understand different techniques.
So you're right, there is value in exposign divers to other equipment styles if they're interested - the majority of divers aren't gear heads and don't care much.
But the important thing is timing i.e when to introduce further and additional information in a way that doesn't overload them nor detract from their learning.
Hope that helps.
