I upgraded my Greggs to Protons two days ago, so I thought I'd add my opinion on them for future readers. I got mine from Indy Superbikes for $79.
First and foremost they are indeed as bright as everyone claims they are! I temporarily blinded myself and then did the same to my wife when I asked her to tell me which flashing mode she liked the most. No joke when you look at them dead-on.
The fit could be a little better. The beveled back edge which fits into the opening in the fairing isn't perfectly sized to fit the opening. The overall light isn't big enough to overlap the opening on the outside of the fairing so I found that no matter where I positioned them that there were tiny gaps between the light and the fairing. That sucks. The Greggs had the same problem, but because their exterior bevel overlaps the fairing opening by like an 1/8" you don't have this problem. To help keep dirt and water out I put a tiny bead of silicon around the edge of the light on the inside of the fairing before I put it all back together.
The fastener is just a single large washer and a nylock nut. I added some blue Loctite as well knowing how much shit vibrates on this bike. I didn't trust a single nylock nut to stay put, especially when you can't crank the piss out of it to tighten it down (or you'll bury the washer into the fairing). Here the Greggs kind of beat it again where they used three small allen hex bolts and washers that you tighten into the light.
Every other category the Proton's win over the Gregg's, though. The wiring in generous, a smaller gauge than the Gregg's (easier to work with), and you can configure these to light up pretty much however you want! I only attached the ground and orange wire for the normal flash. My second pick would have been the fade effect. The strobe blinks too fast, in my opinion, and I think it would be less noticable. I wanted the light to be on longer so that's why I stuck with the normal mode. I did leave the other wires in place but shrink tubed so if I ever change my mind later I can't easily change the flash modes.
Here's two easy compare pics between the Greggs (crap brightness) and the Protons: