Salt grinders often have softer grinding mechanisms than pepper grinders as they use materials (steels, nylon etc) that resist corrosion. Its said that pepper being harder can damage salt grinder mechanisms.
That said I use cheapo Ikea grinders for both salt and peppers and don’t observe much difference - and have used the same ones for 10+ years.
I use my grinder for everyday sea/rock salt and find it good for grinding the lumps - I can change the grind quite easily. I don’t use flakes in it as moisture makes them clump better to use the straight from the packet.
I do use a number of grinders - black pepper, white pepper, and various other petters. Sometimes I put various spices through them if I feel it can add to the dish and I can be bothered to get the coffee/spice grinder out.
