I don't see the issue...
They want it for an inlet kit...hardly car threatening to a company as well respected as Forge.
People are happy to fit aftermarket HIDs, different springs, wheels of questionable quality, lowering springs of unknown poundage etc...do you think they have all been R&D'd properly?
At the end of the day, if you design a replacement part based around the space available and try it on the dyno...it works, or it doesn't.
I'd be happy to lend them my car for 2 weeks if I lived more local.
Forge have fabricated several one-off/special parts for me over the years, and I've never been anything but impressed by their attitude and service.
Only one thing concerning me...
Forge tried to make a Mk6 version of the Twintake a couple of years ago, and couldn't get it to make any more power than a more traditional inlet kit...so I'm wondering why they are having another go at it?
As for the gains, the Mk5 GTI uses a different inlet set-up...and the Forge Twintake gave a dyno proven gain of 14-18 BHP I think, on a mapped car.
There are too many independant dyno plots proving proper gains for it to be a fluke.
But, I did hear from someone within Forge that the Mk6 Twintake didn't deliver what was expected.