Good question Sapper...I installed a plastic runner in a home on the stairs leading down to the daughter's basement bedroom. You should have heard the fireworks from the dad! It honestly smelled like someone was smoking weed!!
All new products have a distinctive smell but they dissipate over time..sadly, this is true of that "new car smell".
I'm surprised that the heated floor element is a foot below but that is inconsequential at this point. You can purchase an underlay which incorporates a vapour barrier.