Just got the P1's.
A quick check shows that with the projector/halo fogs I bought, if you remove the projector these fit PERFECTLY inside the halo and in the existing bracket/holes. All you need is about 1/4" worth of spacers and slightly longer screws than it comes with. My buddy has some shrouds that fit perfectly in the housing, too, so the P1 projectors + shrouds may fit like a glove (I took out the halos...not a big fan).
Honestly, after closer inspection, externally the projectors are identical. They obviously share the same manufacturer. But the ones that came with the halos have a cheap, flaking chrome finish on the front of the cutoff shield, and the lens is not as clear or high-quality looking. Very interesting. So, the short version is you can get these halos, (
http://www.ebay.com/itm/01-YUKON-DENALI-SIERRA-DENALI-HALO-PROJECTOR-FOG-LIGHT-/130533198014?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3ASierra+Denali&vxp=mtr&hash=item1e646288be ) easily take out the existing, pre-wired, non-HID projector, and sub in a P1. It's a matter of taking two screws out to do it, and the fit will be perfect.
Comparing the P1 output to Blazers and Fusions tonight, but from a pure fitment standpoint, these P1's are going to be simple. I don't even need the mounting bracket they came with. I'm hoping the output is as clean and sharp as the Blazer.