Tried with an IP allocated to a major wireless network operator. It was far off but also ran out of credits when trying with higher limits on subsequent attempts.
Seems tool is relying on ICMP results from various probes. So wouldn't this project become useless if target device disables ICMP?
I wonder if you can "fake" results by having your gateway/device respond with fake ICMP requests.
I talk about it a bit in the article. The easiest solution is to use the last available hop. In most cases its close enough to properly detect the country even if the target blocks ICMP.
Email me if you would like to get some additional credits to test it out, dakulovgr gmail.