How much more difficult it is depends on how active a person is in their FW
fish keeping. The SW
tank should be tested everyday for amm, nitrites and nitrates for about the first 2 months, maybe a little longer, depending on how long the cycle is. After that, weekly should be ok if water params are stable and good. Other than that, it's regular PWCs.
But some FW
tank owners don't test their tank at all, and some set the tank up and add fish that same day. SW
should be done slowly and the equipment, fish and coral aren't cheap at all.