Thank you for making a post.
Currently, there are several devices that are confirmed to work with Avenza Maps such as Trimble and Bad Elf. The article, Connecting to an External Device, have instructions for several devices in order to connect successfully.
Here are several External GPS Units that have some documentation.
While Avenza Maps does not have full coverage of all external GPS devices, there have been some devices that have worked that we have not listed.
I would give Juniper System’s video Connecting the new Geode to an iPhone | Field Ready a shot to test the compatibility (if you already own the device).
Please let me know if you have any questions.