Comment by rolfvandekrol

The amount of possible alterations (practical alteration that people actually come up with) of a diceware passphrase is, I think, much lower than the possible values of a 6 figure number (which is what most two factor applications use). If you think hard, you'll come up with maybe 100 possible alterations. I wouldn't trust this scheme as my password manager. I use 1password, which feels a lot safer to me.