While the phrase Semper Gumby does apply quite well to the sea year, one thing that I can tell you is that if your DS decides to go out with MSC he will be able to give an availability date for when he would be first ready to ship out. This could be a couple of days after graduation, it could be two weeks after graduation. The relationship between the ATRs and MSC is not very good, and MSC is slow on most matters, which doesn't factor very well with the tight schedule of the Academy. Every 2013 B splitter I know who went MSC and gave an availability date a week or so after graduation didn't ship out until late July/early August. The trend continued with 2013 A splitters, so if you want about six weeks with your DS, this would be a good route. However, the lack of sea days will make second sailing period difficult, trust me.
I'm not the person to talk to if you want to hear good things about MSC, but if your DS is interested in the Navy or MSC and wants to sail with the fleet, know that you might have him home for part of the summer.