Having seen both, I barely see a difference other than two specific points. The opening credits on the Radiance seem to have been modified at some point, while the Criterion appears to use the original. There's a short section about ten minutes in where it looks potato quality and I think Criterion makes it look very slightly better. Clearly isn't an encoding problem, but it's as if there's a short section that only exists as a dupe of a dupe.
Criterion BD:
Radiance BD:
Criterion BD:
Radiance BD:
and here's one of the first frames of the first shot after the credits...
Criterion BD:
Radiance BD:
and this is the "potato quality" shot I mentioned just a few frames apart (from the Criterion BD):
Didn't bother grabbing the same frames from the Radiance since it looked practically the same. Other than these two sections, the Criterion 4K is gorgeous, as is the Radiance. Happy to own both since they have unique supplements, on top of the other two films in the set.