Hi David,
Thanks for your prompt response, positive feedback and advice. I'm afraid I had to look up the GBS Zero, but it looks great and must be good to drive. I rented a Caterham 7 wide from Caterham for the day with a friend a couple of years ago, and had a great day out, which helped me to decide on the Brooke.
As commented to Blue, my seller's advice seems to be correct, so I will go with that for the time being.