Completely agree which is why I made the caveat on my previous post that I was playing devil's advocate.It's not just about efficiency though, is it? I have a G40 which cost me almost £1100 - I could do decoction mashes with a saucepan, a plastic bucket and a blanket, which would have saved me a shedful of money ... and driven me insane. Spending money on kit we can afford is part of the pleasure of our hobby, and for me the GF grain mill does not have to save me a penny to justify its purchase.
If the reason for buying is for perceived cost benefit then I don't think it works. But there are a whole host of other reasons you might want to buy a grain mill such as controlling efficiency more consistently or the simple pleasure of doing it yourself.