The old and dumb one first:
With this card... why would you ever activate the R ability? Unless you wanted the copies discarded. It doesn't say "playable by your opponent" or anything.
The newer, less-dumb one... Slim and Athletic sez, in brief, "After a player gets momentum, they discard it instead." If an Ira-Spinta E is played and the momentum is discarded this way ( instead of being added to momentum) would this make the ability fizzle because the costs were not payed?