The EK wifi offer is probably the most generous of any airline that charges (wifi is free in F on the A380 for QR passengers).
$1 is minimal, and 500MB pretty good considering the speed offered - you certainly couldn't download a tv show, but for general social media and their respective Apps, it's fine.
Email works well too, but it can be a bit slow.
Also bear in mind that WiFi will not be available on the entire route - as certain countries are black out zones (Iran, Iraq, India etc).
M