Interesting pictures with accompanying texts.
Looks like they were taken from a workshop manual but I don't recognize these from any of my manuals.
I interpret these reviews as a personal reflection and unfortunately I can't agree.
When I finally, somewhat reluctantly, decided to complete my bike collection with an R1200GSA K25 (I needed a bike with a large tank volume) I had ridden a few examples and knew what I wanted.
The reason I was a little hesitant about a GSA is that I have always had difficulty with the telelever that BMW insists on.
I can stand it even if I don't really like that solution, I prefer real front forks.
But engine-wise there was no doubt for me, it was the twincam that I would have.
The older R1200 "hex head" has a very nice engine that unfortunately feels a little reluctant closer to the rev limit.
The difference in active driving is big when you then drive a twincam, which is not only a low-rev engine.
At low revs they are identical in my opinion, I can't tell the difference between them when driving slowly.
For me a twincam is almost like a KTM LC8 when you drive actively, very fun and entertaining.
And a TC almost as nice as a well-adjusted airhead when driving at a legal pace in e.g. city traffic.
There is no time I would choose a hexhead over a twincam if all else is equal, but of course I would rather buy a nice hex than a bad TC
Just my opinion, based on how I experience the difference between these engines.
Best regards