In reply to Tonybhoy:
I bought a Magene USB ANT+ from Wiggle (thinking it was necessary) when I bought my smart turbo before Christmas. Then one day I started using Zwift and realised that the dongle wasnt plugged in but it was still working - the laptop had just connected using bluetood, doh!
Having researched more, ANT+ is really more for sensors as it is lower power, bluetooth will give a better connection (particularly indoors where you might have other interference) but is more power hungry - but thats obviously not a concern on a turbo or laptop.