Just wanted to post my experience with hooking up a Humminbird ice ducer to your average Humminbird portable unit.
I recently acquired a Humminbird Piranhamax 197c along with a Humminbird ice ducer and upon turnning it on, my head unit was displaying "Transducer not connected". At this point I started getting a little worried that the unit was not compatible especially since it was not listed as a supported unit on the list of fishfinders to begin with.
After a bit of research, i found out that a Humminbird transducer for a boat will have 3 pins in the connection and one of those pins is what tells the head unit the water temperature as well as the fact that a transducer is connected. Humminbirds ice ducers however, do not have that temperature pin due to the fact that surface temps in the winter will be relatively stable in the 32f range so it just doesn't require it as much. So without the temperature pin, the unit does not know that the ice ducer is connected and will automatically go into simulation mode.
To override this, simply turn the unit on and immediately select the normal mode and like any other transducer, it should start to give you a signal, and in my opinion, a stronger signal than the summer tranducer.
So if you have an older Humminbird kicking around, don't be afraid to experiment with the ice ducer even if there's nothing indicating that it's compatible. If the connection looks the same, it should work.
Hope this helps a few people having a hard time dishing out the $600 on a vex.
Flashers might be slightly more sensitive and less delayed but my graph can pick up a panfish jig no problem and is only maybe a second behind real time and i like the amount of layers and colors a graph displays as opposed to a few bars on a dial.
Feel free to ask me questions about the setup, it will change the way you ice fish if you haven't already tried a sonar on the ice.