Should I let my friend fit my new Edinburgh kitchen, or hire a pro?
Absolutely the latter. Unless your friend happens to also be a kitchen fitter, you should hire someone who does this for a living. Kitchens are highly specific rooms that must be very carefully built and layered. I recommend that you turn to a specialist in kitchen fitting who can do the job instead. Indeed, there are many Edinburgh joiners who you can easily hire to do the renovation for you.
Hiring a professional might cost you more money, but anything you spend you get back peace of mind. A kitchen fitter will cover the cost of damaged materials and supplies; your friend will not. They will also be experienced, insured, and come with a history of doing the job. In short, your friend might mean well but unless they are a pro, avoid them!