Brigid has many disadvantages but can be very powerful if you know how to use the spells, Here is a very good blog post by Draenin highlighting the advantages and disadvantages to Brigid.
http://forums.graalonline.com/forums/blog.php?b=73
Kinda going off topic so I'll get back on it.
Brigid can be very disadvantaged in many cases which is a pain but Brigid has only ever been great fighting bile users.