No slippage. Since I only have it for 2-3 weeks, I actually used the power from the trainer rather than from my power meter when connecting to Zwift. It was out of lazyness, I wasn't doing high intensity anyway.
Today I did a comparison by logging the powermeter data on by garmin and the trainer on my zwift.
Thinkrider vs Quarq: 274Watt VS 280Watt average (about 2.5hrs)
The pink one is the quarq, the blue one is the Thinkrider. Looks like there is an slight undershoot at the high power. My takeaway from this data is it's quiet ok. It's a big improvement over my 7 year old Tacx Neo which gave very pessimistic power data.
An important remark is that nothing states that my Quarq provides the truth.

