Not great. The new models (PopGrips) advertise themselves as supporting it, because they're easy to remove with a twist (which defeats the convenience of wireless charging.) I still use it but 1) my popsocket is mounted flush with the bottom of my case, 2) it only works conveniently on a vertical charger[1], as they're narrower than flat pads[2] and 3) the phone has to lie horizontal so the PopSocket hangs off the back.
I did just test it vertically and it seemed to work if the PopSocket itself hung onto the lip of the charger. I think this might affect the charge rate, though, due to the distance from the coils.
