It's pretty reliable if you keep it safe from physical damage
yfw paper and pen is still much safer than any of these password managers
one vunreability in your shitty app and all the bots on the internet be capturing your accounts and asking for ransom money
its some some ups and downs.
Your physical location is must less likely to be compromised than say the one of the dozens of sites you might have signed up on.
But people tend to make shitty passwords usually
I use lastpass personally.