It doesn’t really provide anything useful for Cellebrite and it only works on older devices.

iPhone X is barely 2 years old. It works on the vast majority of iPhones in use today.

For those it allows complete data extraction except the Secure Enclave, correct? I suspect this would have been valuable.

If you have a passcode, all of your data is encrypted with keys stored in the Secure Enclave. So this alone won't let you dump the contents of a phone. (But it's a useful 1st step vulnerability to others)

Every iPhone since the 5S has had a SEP, meaning, as this researcher points out, that checkm8 doesn't do much for Cellebrite for those phones.