High mass and low mass response times

High mass is slow to heat up and equally slow to cool down.
Low mass is quick to heat up and quick to cool down.
It is true that in a concrete high mass installation response might take a day or more to warm a room from fully cold. Plates above sub floor might take 1 hour or more. No plates in joist space might take 3 hours or more, but in the real world after your home has initially warmed up - Response time rarely matters. Outdoor Reset Is effective in anticipating heating requirements by monitering outside temperatures, Like making your thermostat smarter.

Thermal striping.

It is true that you can feel a striping effect which can vary with type of installation. This can be noticeable when the floor is initially warming up from fully cold. Once the system is up to temperature typically the surface of the floor temperature will be only 75-85 F. This Low temperature is all that is needed to heat the space and thermal striping is not normally noticeable.