I use a keggle for a mash tun, and direct fired it until recently. I had a simple (yet pretty strong) false bottom with a drilled hole for the dip tube....worked like a charm. The false bottom you indicate looks kinda flimsy until you see the supports....the supports look like they give you a few extra inches of height and would stand up to about 50 pounds of grist, which is good, but for $75 you could probably go with a thicker material one and not need the supports.
All things considered, it looks good, go for it.