Topband: Extra isolation transformers?

[Dan Zimmerman N3OX]

Any reason not to use a 1:1 transformer wound on a Fair-Rite
2873000202 instead of a conventional feedline choke to get extra
common mode impedance for my flag feedline?

I'm not phasing it with anything so I don't have to worry about
accidental phase inversion.

Is insertion loss an issue?

I wound the flag transformer on one of these cores and measured
(inaccurately I'm sure) about 10pF between the primary and secondary
windings.  I'm sure I can do better with just two turns on either
side, so it seems like a cheap way to get an extra few thousand ohms
of isolation.

Any thoughts appreciated.  I've got some nasty local QRM this season,
unfortunately, so anything I can do to keep the flag pattern clean is
important.

73,
Dan