The benefits to both are somewhat different. The mk4 was and is proven to be a much less rigid chassis than the mk5. The mk5 was after all the GTI's great comeback, as I'm sure we all know!
This device was initially developed with the mk4 in mind to resolve an inherent problem and it may be fair to assume it met the designers specification and requirement since development and manufacturing will have cost money and it had a successful market launch.
The debate here is the effectiveness of the porting across to other platforms and the separation of this from marketings base principal - supply and demand.
Destructive testing would prove ultimately which is stiffer but this is fails to test the car as a new quantity. You would simply be checking to see that an effect is present, not how it has affected the dynamics of a complete car. Therefore testing of this type is pointless. Far better to put the car in the hands of a skilled test driver who is capable of technical analysis in the right environment.
Quote: 'When it comes to reviews, I think if you were to waste a bucket of money on something you would just keep quiet about it.' - This is exactly my point, and were it not the case then the value of honest revues and forums would increase x10 fold.
I'll be happy to be enlightened with an honest revue, if of course everybody who has one doesn't keep quiet
I do trackdays at Goodwood fairly often, if I offered you a session as a passenger I'm fairly sure you'd step out of the car convinced it was absolutely fine, thank you very much. For me I would want to see before and after lap times and comments on feedback and handling from a pro driver.
My point is feeling a difference might not amount to making a positive difference. They're not mutually exclusive.
The mk5 is a stiff chassis to start with with softer more customer friendly wider market appropriate peripherals bolted on to it, so consequently it responds well to some changes. The mk4 however was a soft car by design and so has much more fundamental chassis issues to overcome.