So you can replicate your road riding positions while you train.

I don't know about the power measurement on this specific trainer, but it's much easier to determine power on a dedicated trainer (not a friction driven trainer that you attach a bike to) than a bike because the trainer is providing the resistance, not the variable wind, aerodynamics, tire drag, or incline that you are riding up. On a bike you must measure the torque be applied at the crank or wheel. On a trainer, you can simply determine the force applied on the drag mechanism. This can measured, or calibrated. Calibrated force with magnetic drag mechanisms is much more straightforward and less problematic than with mechanical systems. So, I'm saying it is possible for power to be reasonably accurate on this trainer, not that they've done it right and it is.

This entire trainer costs about the same as a power meter for a bike, which suggests it would be unrealistic to expect it to include that kind of power measurement.

And of course the only thing this trainer has to do with the TDF is that they paid Amaury enough to license the logo.