Is Archi Steam Farm Safe?

Well the login info is stored locally on your machine, so if your computer gets infected with malware or whatever then your account is at risk.
Otherwise, I don't see why it shouldn't be safe. ¯\(ツ)/¯

I've been using it for years without any issue, although I only use it on my card farming alts because I don't like messing with my "time played" stats on my main account, I like them accurate.