The fb in your link has smaller holes. My holes are 6mm in each ss layer, the resulting holes with the two layers one above the other are then ovals 4mm X 2mm. Different approach, in my fb the surface for the grain bed is not flat. Cannot say definitely "it's better!", in my idea it should work better. Not enough experience to say I'm right.
I went with 3/32 holes on 5/32 staggered spacing which gives me a 32.6% open area; the material is 1.5mm thick. I'm quite happy with the hole size and total open area. Your material definitely has some pretty large holes; I see the need for the double-layered approach now. I definitely like how much more attractive your design is by welding the perforated sheet in the center of the ring vs. directly to the top in the Malt Miller design. -I also like your use of the 2nd ring to help provide extra support but I think give that my MT is only 50 liters and the material is 1.5mm thick I can probably get away with a single ring. (I'll try it and if it starts to bend after a batch or two I'll come back and add extra support later.)
I'm not sure how thick to make the bottom ring. I've read that the less space under the FB the greater the efficiency (I don't think this applies in a recirculated mash system, though), and I've also heard that slightly more space will help decrease turbulence under the false bottom... I think I'm going with a simple 1" ring (I have to order the ring material today).