Surely with this hat you don't have any access to any GPIO?

Unless i'm missing something - which is where i'm like why not just buy a NUC with similiar RAM for far less.

You do still have access to the GPIO. This HAT [1] stacks on top of the GPIO connector but passes through all the pins so you can still use them. This one is connected through PCIe so it shouldn't be blocking off any pins from use, unless you wanted an NVMe SSD hooked up!

[1] https://www.raspberrypi.com/news/introducing-raspberry-pi-ha...