Hi GolfTi.
Spoke to Dominic at Superchips today. I think he is the owner.
It would seem that the latest GTis cannot be re-mapped through the diagnostic port and the ECU has to be physically removed for a re-map. Therefore, and very unfortunately for me, Bluefin cannot be used. The cost for this new way is the same and there is a mobile fitter who can do this. Not all Superchip agencies are able to re-map in this manner anymore as they require different software and training.
Dominic was not sure when the changes took place but as we have gathered from knowledgeable members, it was probably after BW44/45 last year. So this counts
Wolgang out as he was BW7 this year. Lucky Wolfie.
The other thing he did suggest, which you had already, is to try Bluefin, if it works great, if it does not then return it with full money returned. He also mentioned that the power boost was around 44 bhp.
Then, this late afternoon I spoke to a master VW mechanic who said that VW hardly ever check if cars have been re-mapped when they go in for a routine service. However, the new system will physically need the ECU opening which they can see. Now it also transpires, that some cars might have also slipped through after BW45 which can be re-mapped through the diagnostic port! However, I am sure mine is not one of them.

Needless to say I am really jealous of the flexibility of your system.