I tried spoofing GPS with Niantic's Ingress game, just about the second time I played, and the spoofing apps relied on the fake location flag in the dev settings - of course Niantic checked to see if that was set and refuse to work if it was [until the system was rebooted, with the flag disabled, AFAICT]. Haven't tried with PoGo as I'm more interested in playing it [with my kids, honest!] than working out how it works.