Don't worry the CFI at Border knows what he is doing.
I am sure it will be 100% legal and you have nothing to worry about.
There are changes for the flight training industry in the not so distant future which changes the way that they can operate. We arn't 100% certain when they will come in, but they will eventually, current date is some time in September.
I expect Borders training manual will be a work of art and they might very well get approval for operating out of Oban, phone them and ask for the CFI and ask.