MichaelLAX

My recollection is that when it is in the "GMRS" mode that comes from the factory, there are only a limited number of programming channels that will allow alternate CTCSS and/or DCS tones and still transmit:
Channels 1-22 can only transmit simplex; 
Channels 23-40 can only transmit with the +5 MHz offset already factory set (so not simplex).
Channels 41 through 500 cannot transmit.
If you do this, you can "open your DB-20G" to transmit as you want to program (remember the FCC rules for frequency and power output as well as narrow vs. wideband), as well as find out your firmware version:
Turn off
Hold down V/M key
Turn on
Write down Firmware version listed on the bottom line.
If you want to "open" your DB-20G, do this:
Using the Up and Down Keys, change the Mode from GMRS to:
(136-174)
(400-470)
Now turn off.
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You can also accomplish this in the Radioddity programming software by clicking Model -> Model Information:

You are correct: the Amazon page and reviews are full of misleading and outdated information. 
I purchased mine for $99 from Let'sGetReady with free shipping and a $20 dual band mag-mount antenna for my car (plus a $25 cup-holder mount from Amazon).
I now have a 2nd unit in my shack connected to my rooftop Comet tribander and it outperforms my Yaesu FT-857d on both 2 meters and 70 cms. 

That radio requires an antenna with a SMA female connector at the bottom of the antenna.
UPDATE: I may be wrong about the SMA gender needed on the antenna  
A popular favorite a boost in receiving/transmitting is the Nagoya 771-G (Be sure it is the G model, cut for GMRS). But this antenna does not collapse and probably must be disconnected and put in your backpack while you hike.
A popular collapsable antenna with more gain is the Smiley Super Stick for GMRS
That is a dual band receiver, so if you will be listening to VHF, I recommend a dual band antenna.