I tried Zwift for the first time yesterday on my dumb Cycleops Jet Fluid Pro trainer, speed and cadence sensor only. I can definitely see the potential and it made me want to buy a new laptop with a better gpu and a wahoo kick'r! Too expensive for my blood though

Would having a heart rate sensor help with calculating the correct speed or is there no need to bother as a power meter is where it's at?

Also, is there a way to display speed in metric (km), not miles?