The PG manifold is definitely a PITA. And this is coming from a guy who works on cars for a living. The biggest pain in my opinion is not being able to turn a couple of the exhaust manifold bolts more than a 1/16 of a turn at a time! Overall it took me about 3 to 4 hours if I remember correctly. I've had it on so long now I've forgotten.
As to the perks of it. It sounds awesome. It's very tasteful and not loud at all. You can definitely hear the turbo spool more clearly and it does so much faster. Plus when you remove the stock mani and set it next to the new one you will be very glad you're getting rid of that hunk of junk! The only real choice would be between this mod and the corksport catless dp/rp. All I can say is I'm installing the downpipe tomorrow! So get both!