Rolls......, Rain is not dangerous, but a monsoon can kill you....
Citric acid is fresh water for rust stains like that, and the lemon juice has little concentrations of it, for what concerns dangerousnees of hydrofluoric, it's not like you are supposed to use it pure, any acid or alkaline stuff is potentially dangerous if pure, even cloridric acid you also find in limescale cleansers like viakal etc... if in bigger concentration will not remove limescale from your toilet, it will totally melt it, just think we use 90% solution in our company to make pure gold as it dissolves all metals except gold, also have you ever heard about mafia using it to dissolves bodies? Could you do that with Viakal???? LOL
But in fair concentration will get your bowl clean, and is safe any use for which domestic/cleaning is supposed to be used to...
Same is here, the product I linked is perfectly okay to be used on clothing and even colored ones, as you can read, but it's an acid and it is best to do not let it sit too much and you got to' flush it immediately from clothing, so you bettter alteady fill your machine before for the 2nd wash, the product has a concentration of 15% acid, if I remember correctly.
If it was not so, it would melt your item not only remove rust, sure is that it is a chemical, and you have to use precautions, ie use gloves if your skin is delicate, avoid stiffing it in your nose or drops to reach your eyes....etc...
Pretty much all things that a normal functioning adult would do, and like you do for any other chemical you use in your household...