I'll be interested to see what people have to say about this as well. My son will be 20 mos when we cruise in three weeks. Flounders isn't an option for us because I'm a stay at home mom and have never left him with anyone. We're planning on taking it easy, lots of playtime at the beach, etc. >
IMO, you can have a great time even without using Flounders. My children are almost 7 and 19 months, and we are sailing on 11/13. This will be our 5th cruise, and the third time we're sailing with a child under 2.
We've never used Flounders, and we've always enjoyed ourselves immensly. We fed our kids about an hour before our seating so they weren't starved; we had fruit cups waiting for them each night; we let them color and/or bring a small toy to the table and they did great during our meals. I've never had to leave a dining room (I've just jinxed myself, I'm sure!) because of a squirmy child.
Each year we do our own thing at each port, rather than book an excursion. I'd hate to feel pressured to do something if one of my kids was having an off day and would rather relax on the ship. That works very well for us, and I'm looking forward to doing that this year too, in St. Maarten and St. Thomas.
I also wanted to say that some days at naptime one stays in the room while the other has some alone time. Last year I really enjoyed going up to the adult pool for an hour or two, and as a trade off, my husband went to the movies at night (something I am not interested in dong) and I stayed in with the boys.