If one gets this card early, it somewhat functions as a removal option for weaker monsters that may have some annoying stats you want gone. However, as the text suggests, this is not a removal card. This is a card that inflicts 5 damage to a creature. Threats that you may want gone can easily survive a hit from this grenade, and can still be a problem card, especially if it could regenerate by whatever method. It's more worth it to make the room and spend an extra resource for fatal blow for 4 resources. Or Imperial assassin and it's assassination effect.
but still, if you happen to get this card early, it can still function as a removal card, until decks start getting more advanced from players or bots. Then it's time to look at other options.