Yes I have done it.
I would have used Martin too but couldn't get up to see him.
Most mappers are just file suppliers so make sure you use someone reputable and Maryn is exactly that. Loads of happy customers on here.
I used someone local to me who came to my house as I had no time to travel. The ECU has to come out, opened up and be bench tuned. Ford have gone to great lengths to prevent remapping. There is also a metal guard over the ECU with shear bolts. They have done this as once you realise there is no physical difference between the different states of tune 125, 155) lots would be tempted to remap.
I used a Vieszu file supplier, the skill is in applying the tune in a very controlled manner. The voltage has to be held at an absolute constant during the write and read. So using someone who is very familiar with the process is vital.
The results are excellent over the stock tune though, so well worth all the trouble.