I just saw same-color PEX yesterday in a hydronic system. (Fittings at copper were leaking BTW). That looks like PEX to me. Next time, wipe off the gravel-dust. The letters PEX are printed on PEX tubing. As for in-slab radiant heat, there are pros and cons. One 'con' is that in some cases, due to the 'flywheel' effect, you can actually overheat the space. I've run into that a few times when folks used in-floor radiant heat and then had huge parties on those rooms. All those 98.6 'heating units on legs' coupled with that thermal mass radiating-off heat lead to the homeowners complaining about having to turn-off the radiant heat. "Heat goes to where it isn't" is the heating guy credo... Heat from that tubing is radiating full-blast up/down/around, conducting into the soil/gravel/concrete, etc. You get the picture. It's a case of 'depends on the circumstances" (of install, underlayment of reflective materials, soil composition, installation layout, etc, etc., etc). The orginal poster here may have missed the fact that 'just heating the floor' also 'heats the room' via 'radiant heat' (floor 'giving-off' heat to the other things in the room---including people).