True, these pets can shield you and heal you which is great, but I noticed something very annoying. If your a sorc, like myself, most likely you'll have your own shield blow casted already, the thing about this filidh is that it will try and cast the greater aura shield on you, but since you already had YOUR specific shield cast, the damn thing will continue to cast it thinking it failed and try and try and try again. It gets annoying because sometimes when you command it to attack it won't, it'll just continue to cast the damn shield on you.
Now if you decide to let the filidh cast the shield, well it has a VERY LOW buff from the shield you would have. Example, at lvl 9 I had my shield valued at 51, when the filidh casted her shiled on me, it valued at 15, so your chances of dying increases, I don't recommend charming this one if your concerned with shield protection.
If you charm one of these they will cast a shield buff on everyone in the party. Plus will heal you when in combat, if they are not being attacked, if you drop below half hit points.