Yes,its all about setup really,but roughly for 5v5 felguard is great,for 3v3 can be good and 2v2 its not good.Felguard is great against clothies,interrupt vs healers and intercept,but vs high armor classes its a joke.
You can use it despite that ofc.deep aff is good because your dots wont be dispelled,you have insta howl of terror and shadowburn if you spec for it.