He said that it is not illegal to use blunt knives, but just that if people see you in the park training, they might think that it is a real fight with real knives, and so become afraid. If most people are using uniforms, and rubber knives are used that might be helpful. But if all the people are wearing clothes that arent uniforms, then the police might even think it is chinese gangs fighting in the park, cuz the triads HAVE fought eachother with weapons in public before.
Like he said, there is nothing illegal in it, its just Irish society generally doesnt have public displays of martial arts, so any fighting they think is real. So using rubber knives, might be the way to go, because they can not be mistaken for dangerous weapons.
So that means if the Garda give you grief under s.9 of the firearms and offensive weapons act 1990, you can state same act allows for reasonable possession.
Hope that helps"