Safe and working, but I'd add this: First, if you decide to use it, it's usually wise to disable automatic downloads on your PS4, so that it stops downloading and installing new firmware for your PS4 the second it's available. Sometimes that new firmware changes save file structure and makes it so that SW doesn't work anymore and it takes a couple of weeks for the SW team to catch up so that things are working again. There's also no guarantee in any given firmware update that they'll crack the next new save file structure change, so you upgrade firmware before SW gives the "all clear" at your own risk (risk being that you might not be able to use SW any longer). This is usually just a problem with the rounded-numbered updates, like 5.00, 5.50, and more recently 6.00.
Second, while it's safe, you shouldn't use any modded saves online. For instance, don't mod a Dark Souls save and then play Dark Souls online, because the game's servers might detect that or other player's might report you and so you might get hit with a Dark Souls-specific suspension or ban. It would ONLY affect that game. Your PSN account would remain unaffected. And for many other games I simply haven't heard of this happening. But it's always wise to play modded saves entirely offline. Plus it's more than a bit unfair to other online players who are playing with unmodded saves, even if you're just doing co-op, because you could be dropping items for a friend he/she wouldn't otherwise be able to get, making that friend OP, then that friend goes on to be OP in PVP modes.