I fly in the Wash. DC ADIZ and often rent a plane with only one radio.
So, I carry a Vertex VXA-700 as backup. It's the only radio I know of
that has the LIoN battery to provide a longer life. It's also smaller
and lighter so less chance of leaving it behind.

It's worked well for me, to get clearance and listen to ASOS before
leaving as well as to get back in the ADIZ in a plane with a busted
audio system. (Radio apparently worked, but mic or headset didn't.)

-Malcolm Teas