If a URL is written using NFCTools on iPhone, iOS will open it in the default browser without using NFCTools, or in the related app (eg Instagram) if there is one.
I find this only to be true when used on the same iPhone where NFCTools was used.
If you try to have another iPhone detect the badge, it appears not to work - unless you use NFCTools on that iPhone, too. I don't have conclusive proof but that's what the evidence seems to indicate.
