I would say that Bleachbit and Stacer are at about the same level of "safe" as long as a person Reads and Follows the directions.
Personally, I find the placebo effect is stronger than the results. Ever run the cleaner and it displays the long list of cleaning and finally yields 142 kbs of freed space?
sudo apt clean and
sudo apt autoremove are most of what you need. Many may prefer to clean out
Thumbnails on occasion; both of which are in ~/.local/share so no root needed.
Personally, I use
ubuntu-cleaner (If I am in a hurry) because it hits those basics without all the fluff and pomp. Running Ubuntu Cleaner does what I just said: Cleans out the thumbnail cache, apt-clean, removes installed package configs. All you need, really.
Preferences matter. Stacer comes with some good charts and graphs and such; but to me it is not a selling point since my conky's display all that stuff 24/7.