Hey I've got a Knightfall 66, and I think it's great. I like that it's pretty transparent, so it just adds more grit without changing your whole sound, something I've found oddly hard to find...
The EQ controls are useful too. They don't have a huge sweep on them, but just enough to add a bit more presence and bigness, plus a bit more chunk on top.
I haven't tried the Dual Knightfall, but I'd recommend the 66 for sure! Hope this helps