I don't have Campagnolo or a 12-speed drivetrain, but I have 3 Uniblock cassettes (12-28, 12-28, 11-34) for Shimano 11-speed freehub, of which only the first is currently installed. The second is a spare, and the third is about to go on my new gravel wheels.

With a mechanical 105 medium cage rear derailleur (RD-5800-GS), the shifts on the Uniblock 12-28 are indistinguishable from Ultegra 12-25 and 11-28. This is my riding impression over the 6 months (< 1K miles) since I bought the cassette.