Being a loop, it
is also somewhat immune to near-field electrostatic interference such as
from nearby power lines (which may account for the lower noise pickup)

Dunno...I consider this to be fictional content...
They may be slightly quieter as far as corona buildup, or
charge on the antenna itself, but not any noise in the far or
near field. If a loop picks up less noise in a certain direction
vs another antenna, it's the inferior antenna in that direction.
Noise is rf, and a signal, the same as any other signal.
If you get rid of noise, you get rid of *any* signal in that
direction and angle. I also consider the magic noise reducing
qualities of the "shielded" loops to be a fairy tale also.
I've done a good bit of testing, and can see no indication that
a shielded loop is any "quieter" than a regular unshielded loop.
The shielded loop design promotes good balance. But good
balance can be had with any loop.
I guess loops are ok, and they are efficient when fed with coax,
same as a dipole, but I usually prefer dipoles on 80m.
If you run a loop for NVIS, you want it all high up in the air,
with no parts dragging towards ground. Many stick loops
in the yard, and some parts will be high, some parts low.
The current distribution is "fairly" constant around the loop,
vs max on the dipole being at the feed point. So you have
more chances of increased ground and clutter loss with the
loops in many cases. I prefer the dipoles and inv vees because
the maximum current point is up high at the apex, and the
ends of the wires, which may droop lower, are voltage nodes.
I'd rather have the bulk of my radiation high up in the air,
rather than spread helter skelter around the yard area.
Often the dipole will outperform such a draggy loop...
But if all the loop is high and well supported, they can
be worthwhile. But still more work for little if any real
increase in performance vs the dipole.
MK