I've worked with MaxMind stuff on mobile IP location - as they guy says it's pretty useless. If the user is on wifi it's not too bad, at least the IPv4 stuff could pretty reliably get the state and often city. I never had any luck with IPv6 although they claim to support it better now.
The big kicker is if the user is on cellular - at least in the US most cell networks are natively IPv6, and they tunnel connections through giant NAT devices. This leads to two interesting effects - firstly the IPv4 address you see on the server is located at some random data center usually on the other side of the country from the user. Secondly, the IP (and therefore the data center) keeps changing - sometimes multiple times within a few minutes. Doing any kind of tracking leads to a device which appears to keep hopping back and forth between California and Kansas.
This Microsoft Research whitepaper talks more about these issues.
(and before anyone jumps on me for the privacy implications of trying to do this - in my specific case it was tracking devices in an enterprise environment for security purposes and everyone involved had given informed consent)