So far I have yet to adapt one of these buildings to foam core, they're really easy to build. Those War Hammer ones are so simple to build I can put one of the simple ones up in less than an hour, and with the base provided they are pretty stable. The more complicated ones like the ones with the offset second stories take a bit more, but still I can have one of them up in maybe three hours, but then I am building a couple at the same time.
As for the Foamwerks Rabbet cutter (that's the pretty blue one, right) I have yet to use mine. My building area is still covered over with stuff since my mother-in-law moved in. It only got worse when she moved out. But I found that Walmart sells a sheet for $4 I have been buying several at a time so I can build some of those buildings they use for War Hammer. Maybe I will get back to work now. Can only hope.