I appreciate Danny's question as it allowed me to pull out that
article, which I had marked for more careful study. I'm not a
transformer expert but two things about the article strike me:

1. Andrew seems to have the transformers connected in the wrong order.
If he wants the 1:1 current balun to operate at a lower impedance it
should be on the 50 ohm side of the voltage transformer, I should
think.

2. Andrew fails to compare his scheme with its most obvious
competitor, the 4:1 two-core Guanella current balun. This would be an
interesting comparison as the Guanella can use smaller cores (did you
see the size of the voltage balun in the picture? Pretty big compared
to the current balun), but the windings operate with 100 Ohms
impedance at each end instead of 50.

But Andrew's scheme ought to basically work, and better than any single
core scheme. I'll bet the experts on this list could help further.

73,
Glenn AC7ZN