I didn't re-read the whole thread but that tends to suggest a regulator with lower drop-out would be required to use 6V as an input. there are such things around, I have some somewhere, I can check what they are if you get stuck.
The economics of using the cheaper component might be less compelling when faulty returns start happening. I,m sure school uses will find them not so durable .
Any prospect of allowing comunity members to get one of your spares to a suitable donation?