When to buy Santa Containers?
1. You like the ships on the short lists.
2. You own a metric crap-ton of tier V and VI premium ships.
When to PASS and not buy Santa Containers?
1. New players. If you buy, random boats are likely to be low tier and not as good a value as somebody with those ships already in their dock.
In summary, buy for the shortlist and enjoy the extras. If you are not a whale, buys beyond those shortlist ships will lead to buyers remorse.