In a nutshell, they suck. I've had 2 different ones and they both
performed terribly, I could hear, but they were both pretty much mute on
the transmit, SWR's weren't bad, it's just the coupling through the glass
(I believe) that did not cut it.

Good SWR says nothing about radiation efficiency.
A 50 ohm resistor has great SWR, and only radiates heat.
A compromise antenna might closely approximate a resistor.

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KC6ETE Dave's Engineering Page, www.dvanhorn.org
Microcontroller Consultant, specializing in Atmel AVR