What engine is in your Birkin?
I have found that the right tuner is worth his weight in gold. My experience with a local guy who's mostly domestic is that he will say yes to everything but you'll pay and results are questionable.
Tuner I used is a member on here and I trailered the car half way down the country to use him and was very very happy with results and how patient and easy to work with he was, not to mention accommodating. (Tom @1turbofocus) With that said, in my case the problem was more so with my car and my ECU/Software (Pectel T2 on ITBs) being difficult and me not having any sort of Wideband datalogging setup.
Whether you find a tuner or not it's still a great idea to understand what the tune is, how it works and what's the entire point of the tune. I'm still in the process of that as well as still in the process of setting up a datalog (very important to you and or tuner to do the right thing).
My other experience was contacting a shop not too far from me in the NE and they, not in so few words, said that your ECU is worthless and we will waste time learning and it and working around it that you will pay for. Your best bet is to swap ECU's to ours that we are familiar with, get all the sensors setup from the get go and get it tuned right. All for a quick sum of I think $6900 or so. I'm sure the cost is right for all the work but that's too far away from what I needed done and the budget I had.
Consensus is, learn as much as you can, setup your existing car to be able to datalog and have wideband and keep searching for a tuner that's right for you.
Edit: I see through your history that you have a Zetec. Tom mentioned above is your best bet by far. Reach out to him and find a way to get to him is my best advice. He's been a Zetec/Duratec guru for decades.