TrickFlow Heads?

I've been perusing some of the different engine builds and horsepower combinations on here. See a lot of Edelbrock heads, Indie heads, and various others being used. Not seeing many people running the TruckFlow heads. Is there a reason for that?
Builds are out there, but right now it seems like actually getting the heads is pretty tough. Like 360duster said, they're still pretty new to the world. Mike at B3 engines built one that made around 600 hp and I can think of several more that have used them.