Peloton Bike (original) is a bit more wobbly in accuracy. Generally speaking, it’ll be about 10-15% off at higher wattages. While there are rare scenarios of 100w+ off, it’s not super common. The Bike+ (newer model) is basically spot-on.
Practically speaking, this is all no different than any other indoor cycling platform you’d be on, such as Zwift/RGT/etc, all of which have substantial issues with people with old trainers/wheel-on trainers/miscalibrated trainers/etc… One of course only needs to spend about 15 seconds on Zwift to see that.