Anyone ever done anything like this? Im thinking about trying it for a few weeks just to see what happens.

I understand its designed for gaining size and such and won't benefit max strength/athletic ability massively although with a bit of extra muscle from a few week block of this will make it easier to gain max strength later?

And how good is it for adding size?

(im talking about the 10x10)

I think Joel Smith tried that German Volume training last year using front squats or something.  I think he posted it on his blog.  I think it was like Jumpcoach.blogspot.com or something.  Any kind of size to muscle will definitely help with max strength, maybe not directly, but when you dedicate more time for max strength/explosive strength later on it will help.  I've never tried it, but see if Joel Smith will tell you how it went, he's on this forum sometimes.

10x10 is a lot of volume. if you can grow and add strength on 3x5 -- and the fact that you're asking this suggests that you can -- why not do 3x5 or 3x8 or 3x10?