On the way back, I spoke with a commercial pilot who was deadheading, on
this issue.
He said that it's not all that unusual to hear radio interference once they
have allowed the devices on, but when they are in cruise, they aren't
normally doing any urgent communications, so it isn't much of an issue. If
something comes up, then they will pass the word to shut down the PEDs.

On takeoff and landing though, the comms are much more rapid, and the
consequences of missing one transmission are much higher. They need to hear
all the comms, not just between themselves and the tower, but what the other
pilots are saying as well. Add to this, the fact that aircraft comms are
AM, which is inherently muddy, and it's easy to see why they take the extra
precautions.