I’m absolutely with sqad on this.
Before you think about whether it is suitable for you and your young one I think you have to consider your fellow travellers wherever you are on holiday. On a cruise this is particularly pertinent bearing in mind the confined nature of your accommodation. The six month old child will get nothing from it (he or she won’t have a clue where you are). But your fellow travellers could be seriously put out especially (as is extremely likely) if your child becomes fractious due to its confinement.
I suppose that makes me a member of the “ Whingebags R Us” club. If so, that’s fine. Too many holiday destinations are completely obsessed with catering for children, often to the detriment of many other guests and in my view a cruise is no place for a six month old baby.