For normal laptops it won’t be so much difference in performance, as LUKS by default uses AES-XT as the encryption type, and most modern CPUs have AES accelerators in them.

For rPi though? Not sure they have an AES accelerator, and if they don’t then it’s going to be a huge cost to performance.

Not only because USB is using a CPU core to operate (because USB uses CPU not dedicated hardware like FireWire) but also because it has to transparently translate and encrypt every access.

It seems like the raspberry actually has zero crypto extensions anyway: https://www.raspberrypi.org/forums/viewtopic.php?t=207888