I tested with the JSON style input and it's very easy from the plugin side, more or less just a single line to get the array. However the 14 double quotes to get 11 characters in is a bit hard to put that syntax on the user. So I would probably just keep this as a last resort.
Having several actions and push the items one by one gets more complicated as I am already in a transaction flow and the array is also connected to a property.
All my actions in the flow is already standalone so I need to setup a sub flow just for this. From a user point of view this method seems fairly natural, just need to understand if the action is an AND or an OR for values(filters in my case).
My current test implementation is a simplified "CSV" method to get all values in one action. There is some special parsing involved, but not that much.
But what I really want of course is a AddAnyTypeArrayParam()