I do have a concern about accidentally hitting the DSC button when handling the unit, will have to see if I can look at one. It looks like the DSC button is recessed and in the back, in that case it would be avoidable.
I have the predecessor, the M-91D. On that radio, what looks like a distress call button is not a button. It is a cover which you have to lift to access the button.
My radio has been almost as much under water as above water. I have configured the float and flash feature so it only flashes. It does not make any audible alarm, and it does not make any calls. (But it still floats…)
It will flash when immersed, even when the radio is switched off. I suppose that can drain the battery over time. I wouldn’t know because I always charge the battery after a trip - because of a more or less unusable battery indicator which shows full battery up until a few minutes before the battery is empty.