My opinion is exactly the same as that of the Nissan R32 driver. I also got these new when I purchased a used Jaguar XF, and they're absolutely shocking. In the dry you wouldn't notice much when pottering around town, but it's clear that they are going to let go with little prompting because it's impossible to pull away briskly - such as when you need to pull into a gap on a busy roundabout - without spinning the wheels. The car has been checked for tracking, suspension, and the tires for balancing and air pressure so everything is set up as it should be.
As soon as it rains it's a completely different story. I pulled away from a standing start at said busy roundabout and the back end slid around. At this point I'm probably doing less than 20mph. As the other guy mentioned, when they let go there's no warning whatsoever, and in manual you'll struggle to pull away even in 2nd gear without spinning the wheels. My car is rear wheel drive and is a 3 litre V6 diesel, so does have plenty of torque and exactly as he said, you get no traction, wheelspin, no lateral grip and worst of all, no warning.
I have to stress that this isn't on a spirited drive, this is just driving as you normally would. And this was in light rain with no standing water. These really are downright dangerous, people are going to get killed, and even as a driver with 340 years' experience and professional qualifications I refused to take the car out again for the next couple of days until my replacement Pirellis arrived.
It's simple - don't risk your life or somebody else's to save a bit of money, because that's exactly what you will be doing and it's just not worth it.