I ran freshwater in my 75 gallon for 2+ years. It was fun. Grew out a very large Jack Dempsey and a few Featherfin cats. I donated them back to the LFS few weeks ago and turned the tank into non-reef (fish only) salt. My motivation was believe it or not, a small Congo Puffer that I had placed in a 10 gallon salt for the kids. He is now in the 75 along with a Niger Trigger and Foxface.
Changing over the 75 was not $ nor difficult. Replaced the rocks with playground sand from Home Depot was the only overhead, along with some Instant Ocean mix. The sand was 15 bucks and the salt mix was 25 dollars.
I am enjoying the salt a lot. My wife LOVES it. She prefers the colors of the fish etc.
For newcomers, the ease of use all depends on your fish/tank size and your filter setup. My Jack was 8+ inches, the cats were foot total. And when you house fish that large, it's like taking care of dogs - lol. They splash, they move piles of substrait (rocks) every night, and they become moody. Water changes were done every week, they had to be. Large fish eat and crap a lot, and when your water turns to garbage, they will let you know by not eating for sure.