Not to start an argument, but 12V is not only 12V. There may be noise on the nominal 12VDC, which is fine if you are running a heated jacket, as this was designed for, but may not be OK for a flasher. I don’t think it should damage anything, but it might interfere. My Garmin is unusable when my trolling motor is running, since it is powered from the same battery. Garmin gives an RF choke to put on the power cable, but it is not enough. The manual says that the sonar should always be on its own separate power circuit, to avoid electrical interference. I am looking into a separate battery for the Garmin, and am going to try an 18V tool battery, with no converter. Others seem to be getting this to work. I can’t use the Milwaukee converter, because I have Ridgid batteries. If this works, I have 2 connector brackets coming for Ridgid, and will build 1 for the boat and 1 for the ice kit.
I don’t think there is any risk to trying the Milwaukee adapter on a flasher, at least not to the flasher. I have heard that you can overload the adapters 12V port, and fry that, but the converter itself is not that expensive.