As it is annual motorcycle inspection month and I've got to get my 3 bikes through, I'm not going to experiment at this time.
I would speculate though, that it could tend to cause alot more heat stress in the center of the headlight lense - could be more prone to cracking especially when some rain drops start hitting it. I don't know how much of the total lumen output is redirected by it back to the reflector shell, but I'd also suspect that the light pattern out front would be more intense in the center and more weak out toward the edges..
Those Germans usually do things for a reason, ya know!