There are two questions here. One is whether the single
blade prop is more efficient than a multiblade prop
producing the same thrust. That's sort of like asking if a
monoplane glider is more efficient than a biplane glider.
Generally, the answer is the monoplane glider is more
efficient, although how much more efficient is dependent on
the details

Todd, doesn't it seem likely that if there were **some** kind of
advantage to using a single bladed prop we'd see a bunch of them being
used?

The second question is whether given a prop diameter limit,
one can produce more thrust with a single or multiblade
prop. That's sort of like asking if you can produce more
total lift with a monoplane or a biplane given a wingspan
limit. Generally, the answer is that the biplane produces
more lift, although not as efficiently as a monoplane with a
longer span.

I refer you again to the WWII fighters (and bombers) which used more
and more blades in order to harness the greater and greater horsepower
ratings of the engines.

Also, biplanes vs monoplanes isn't a clear comparison to two bladed vs
single bladed props. Biplanes always have interference between the
two wings and the wing rigging has to be adjusted to compensate for
this interference, so one wing or the other (or both) are not really
operating at their most efficient angle of attack. Once the airplane
gets moving through the air, the prop blades really aren't interfering
with each other because the blades are describing helical paths due to
the forward motion. There may be some interaction but it doesn't seem
much like interference to me.

Wouldn't you think the more serious interference would be the prop wash beating
against the airplane itself? I'd have thought we'd see more pusher props, but
that's not a common SEL configuration either. I wonder why?