Gittin page 72B and elsewhere- According to the rabbis, oral stipulations can invalidate what would otherwise be a perfectly valid get. In such a situation a woman who is actually married would have what appears to be a perfectly valid get given to her by her husband, and she would think it is valid. Given that, she might "remarry". So why did the rabbis not require all oral stipulations to be written into the get?
The Gemara on 85a states that when one writes a stipulation into the Get, if he puts it before the Toref, the Get is Pasul, because the husband has retained something in the Get. If he puts the stipulation after the Toref, the Get is Pasul mid'Rabanan lest he write it before the Toref. Therefore, the only possibility is an oral stipulation which, as you mentioned, does have a drawback.