You want to make sure that the radio says it supports the "Specific Area Message Encoding" (SAME). This is what allows you to program the radio to receive specifc alerts. Do not concern yourself with "should I get one", or "are they useful?". Get one. <img src="/images/graemlins/smile.gif" alt="" />

With that said, you'll be comparing features for these radios. The basic functionality is what you will be concerned with (unless you live far away from a NOAA transmitter, then reception capability will be an issue)

A few issues:

1) Battery backup - It should be able to have continuous uniterrupted power while the power is out.

2) Number of "areas" accepted by the radio. In more densely populated areas, or where the "areas" are dense, you want to be more aware of incidents that could affect you.

Edited to add:

A simple Google search for "NOAA SAME" this is the first link:

NOAA Weather SAME Information

All the information you'll need for the system itself. Now you just have to get information on models and such.