My personal opinion, based on the experience of having purchased an FTM-400DR for big bucks, is that if you are looking for something used for trail communications, don't bother with digital modes.
It could just be the Northern Virginia, Maryland, DC, and SE PA or SW NJ area, but I have had two C4FM digital QSOs in the two years I've had my 2m radio. Neither were on the trail. In fact, I would gladly give up my C4FM capability for $200 or $300 in my pocket.
I spent a lot of time angsting over which digital mode radio to choose, but two years after making the purchase, I realized it was a waste of time to even worry about digital modes. Nobody you will ever talk to on the trail is going to sit there waiting for a digital mode QSO to break through.
What I have found useful are the built-in APRS capability of the radio and simultaneous dual receivers.
My summary: Digital voice modes are interesting for hams who got their license to be a ham. Digital voice modes are almost totally useless for trail comms because, statistically speaking, there are very few people running those radios, and those that are running those radios are typically old dudes sitting in their backyard or basement, not in an off-road vehicle.
HAM Radio, as you will quickly find, makes you realize how useless your 2m/70m gear is when there's nobody to talk to. If all your trail buddies are running DSTAR, then buy a DSTAR radio. If all your trail buddies are running C4FM, buy a Yaesu. If all your buddies are grabbing Baofengs and you want to just have 2m/70cm capability for the odd case where you have people with HAM licenses in your group, go with an analog radio.
IIRC the ID-4100A is not a true simultaneous dual-receiver like the Kenwood V71A, ID-5100, or FTM-400DR. It can be programmed to switch between frequencies, but can't listen to two freqs at the same time. Not sure if that matters to you.
