I’ve taken this exact power strip on several cruises , mostly Royal Caribbean ships but also I recently used it on Virgin Voyages Scarlet Lady, I’ve never had an issue getting it onboard or had them say anything about it being in my cabin. I do put it in my check bag though because it’s not an essential item I would need in my carry on. So this surprises me that you had an issue.
Everyone I know who only plays card games or table games has never gotten a comp offer from Royal Caribbean, but I know people, including me, who has played slots sometimes only $50 and gotten a comp room.