I used them for a while with Gale but in the end there are more important spells for the restricted slots. I'm ok with the normal familiars.
But nor with the two stronger Warlock ones. They are nice at lvl 3 but later more if a joke. The Warlock is not one of the strongest classes and could need some stronger summons at lvl 10. If nor like the strong lvl 6 Cleric or Wizard summons (too strong), rhen like the lvl 5 ones.