On Monday, February 6, 2012 1:35:23 PM UTC-5, Lars Peder Hansen wrote:
... These seem almost too good to be true; Low cost & complexity, easy
installation inside (non-carbon) fuselages..

Well, you will get two answers to this question:

(1) Great ! No problem !

(2) Antennas don't work so well next to big conductive chunks.
The vertical stabilizer is filled with radio antenna, elevator
pushrod (and sometimes mechanism + balance weight), mass balance
on leading edge of rudder. So, we will not install this antenna
in the fin, and we do not believe it can be approved and/or
work properly. Also antenna should be on bottom for good
reception by ground stations (no blanking by carbon aircraft).

Personally I have a fin transponder antenna on the bottom
of my (carbon) fuselage with an approved installation...

Hope that helps,
Best Regards, Dave "YO electric" (NOT an antenna expert)