There are THREE of them, although I only use SOS - The Wilds and SOS - The Dungeons.
I did not much like the sounds of Civilisation, so I removed it after trying it out.
Yes, they ARE safe to use and, apart from one particular version of Civilisations that was released AFTER I removed the one I had, they always WERE safe to use.
The thing that trashed people's saves with the other two was people removing the then-latest versions of the mods in mass, blind, unreasoning PANIC and continuing with the same save. I never did that. I continued to use Wilds and Dungeons all the way through the time they were hidden on the Nexus and I still do to this very day.
My original character has over 1200 hours on her and has had a zillion mods added and removed, and although I still get script calls to mods I tried for 3 hours in May, 2012, it does no other harm to my game. The only problem that character has ever given me is intermittent crashes due, most probably, to too many conflicting mods and overly ferocious ini tweaks to try and increase graphical quality beyond what is realistically possible, plus always insisting on using at least 7 uGridsToLoad, usually 9.
I only EVER got save bloat with ONE character when I was trying a certain WIP mod, but the author denied all responsibility, so I made sure I never EVER tried any of his mods ever again. EVER.
But you have nothing to fear from Cliffworms.
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PS Unless you have a really good idea what you are doing, always follow the Central Mantra: "Remove a Mod, Restart Afresh" and start a new game.
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