ACT is on the 1.4 TSI only, and only on models manufactured after a certain date (2015MY vehicles I think?). However
this article suggests Audi are planning to introduce it on the 1.8 next year. If that's true I guess it might eventually trickle through to VW, Seat and Skoda.
To answer your 2nd question, it works in all driving modes, not just Eco. According to
this VW page, the two cylinder mode is
"active over an engine speed range between 1,400 and 4,000 rpm and torque outputs between 25 and approx. 100 Nm – a range that covers nearly 70 per cent of all driving states in the EU driving cycle!"