I am the author of that post about the usage of MIDs 
and I would sincerely advise you to create your own MID and do it properly, as if you rely on UE to do it for you, you will have extreme performance hits, as you cannot keep track of the created MID reference, therefore you create one each time you set the parameters. Also, if you have multiple materials with that parameter name, one “set” will set them all, so again, please avoid this shortcut, as it’s a recipe for bad coding practices.