Sorry, I have all 3: LPVleather, Kaufmann and gen IWC. LPVleather is good, but miles away from the excellent quality of Kaufmann or gen IWC. Kaufmann and gen IWC are identical in quality, but Kaufmann is 30-40% cheaper than gen IWC.
Unless you are talking about the higher end IWCs like the Perpetual Calendar or the new Portofino 8 days, the rest of them actually uses Kaufmann straps. So basically IWC = Kaufmann, and getting through the dealer means you are paying a higher price for dealer commission
Anyway I think Kaufmann straps are very nice, but don't see much difference with other good brands such as Hadley Roma. My gen IWCs are running on Hadley Roma replacement straps too and quality wise, they are the same.