Well, basically it's more vulnerable than a normal core wallet.
Because your 12 words can be guessed.
But, both of them have same vulnerability. A very very very very very ... very lucky person can create same address with you and about bitcoin all matters that the public adress's private key.
I recommend you to run bitcoin core wallet and create some public adresses and then dump them and apply them to a payper wallet etc.
i dont think anyone can guess date/time and where exactly im creating the wallet, my only concern is that if it is possible for a collision due to private key did not implement time/date as seed (ie: set time to less than 1990 on computer then generate wallet which collision would never be possible).
im considering brain wallet which seed consist of : todays date, todays time, my name, my email addr, my email pass, my bicointalk nick, my bitcoin talk pass, plus 5 random word.
I think that you would most likely forget the pass yourself. You're better off etching some additional informaton in steel than trying to memorize everything yourself.
guess i can create from data of my driver licence, plus the data of date and time of making the wallet which will be easier to remember is it
it should be fairly safe so long as u dont forget/mixup the string. its best to use a bitcoin privkey as seed for brain wallet.
thats the problem if the private key itself did not take seed from date and time. because time repeat after 24 hours, but day-month-year were infinite, it never repeat.