The Beguiler subclass for Ciphers seems heavily undercooked comparted to the other 2 options. Both the benefitis and penalties are relatively minor changes. What you gain when attacking/targetting someone who's susceptible to sneak attack is so minor, it feels somewhat like a hassle to go through the process of flanking/debuffing enemies. It doesn't feel anywhere as good or interesting as Soul Blade or Ascendant.