I don't know why they claim a 3.5 lbs pull by the description, but on Ghost's website (I looked again but can't find it atm) I remember reading a little bit saying that the connector alone won't achieve the 'advertised' 3.5 lbs of pull on it's own. You need to install new springs to better balance the pull to the 3.5. Otherwise, you just minimally reduce the pull by putting in a new part.
I did my own tests, but I haven't formatted the videos and uploaded them, I intend on doing most of the work for that this weekend. In my tests, from a bench with the various available connectors installed, Bone Stock, Polished and Ghost Rocket. I got about 6.5, 6.0 and 5.0 respectively on an average of 5 pulls. I had the trigger zip tied around the little shoe/lever safety thing and that also acted as a positive stop for repeatability. I had the gauge put on the tip of the trigger, furthest away from the pivot point as possible to gain the maximum amount of leverage and enact the lowest pull I could. This was a best case scenario, when I would let the gauge slip below the stop and down closer to the pivot, the pull could even double in weight. Also important to note that my pistol has about 2000 rounds through it and that all my internals were polished during this test, except the Ghost and new factory reset bar (I had Ruger ship me one new for tests).
I'd say either install it and see if its any better, or just not install it. You do have another option, you could try polishing the internals (without the Ghost) or install the Ghost as is now, and then Polish after a couple hundred rounds of wear-in. Ghost recommends to not polish immediately before or after Ghost's installation. They say to let it wear in a bit before attempting any polishing if you do. If you're interested any in the Polishing, check my How-To in my signature for info.
Josh