4hp isn't a lot...
But on a 93.7hp it's 4.27% from 3-5k... It's OK just rather high HP/Dollar ratio...
I was trying to get it for my SportClassic..
Yeah, relatively speaking - a 4hp gain on a 80-90hp Ducati is nothing to overlook. A 4hp gain or loss on a 150hp gain is not as significant.
I've got sil moto headers on a 900. They are significantly lighter than the OEM, and the overall finish is nicer than the OEM setup (and before installation, I had mine ceramic coated to reduce temps, and pretend that the minimal increase in scavenging would put my 900 2v in pole position... ha!) For performance gains other than in ground clearance or weight savings, they only allow more flow where other necessary motor adjustments have been made.
For larger diameter exhausts, I think of it like: "Great, you can have more flow "out", but if you don't actually have more to flow "out" (as in, you didn't increase the through-put of the motor - more air and fuel in, valve / head job, displacement, etc), then they simply can't offer any benefits - you can't take advantage of its additional flow abilities if you don't have additional flow."
Perhaps its fair to budget for a set of headers when doing significant motor build on the 2v, BUT if its pretty straightforward stuff...I've seen too many builds using the relatively 'decent' flowing stock headers to consider it a wise use of money (better to budget towards wheels, etc...)