Either will do the job, the SGC230 is waterproof and ideal for a marine environment
, the LDGIT100 doesn't have any particular extra protection for a marine environment, and is designed really for ham/land use.
One other potential issue, as the SGC230 is waterproof it can often be mounted much closer to the actual antenna
, which is better, the LDG needs to be well out of any danger
of moisture or getting wet.
You pays your money
and you takes your choice! I know which one I'd prefer to rely on for radio
use in an emergency
However, budgets being budgets, many cruisers use ham tuners without problems, but it's not a generally recommended action.