What has always bothered me about Rogue Sneaking is that The Venn Diagram of ability to Sneak up on or Surprise a creature and the ability to Crit it should not be a circle. There should be times when You can Sneak, but not Crit, Crit, but not Sneak , and times when you can do both or Neither without token equipement..
I would argue that most automatons, and undead have "Vital Anatomy" in the form of joints and connections between motors and muscles, wiring, eyes, sensors etc... that could be exploited as "Vital". I would also argue that most plants and Oozes don't have enough awareness (or Mobility) to prevent someone from Sneaking up on them.
Rogues should be arguing that Sneak is always possible, unless a Creature is Immune to Surprise, can See, Smell, Hear, Psychically or Otherwise Sense where the players are at all times. I imagine the number of creatures with that capability is low. The Ability to Crit the creature based on it's type should be separate to a Rogue's ability to Sneak up on it. "Not All Sneaks are Crits, but you can't Sneak if you can't Crit" never sit right with me.
Under Current Rules, the Critical Bead for Dwarf Fighter and Rogue only isn't the end of the world, but you're making a UR for only 2 characters to use an ability that would benefit all. and leaving out a character class that also has a class ability that benefits on that ability to trigger, exactly the same as the Dwarf Fighter (Polymorph Druid). "Fighters" on the token... Makes no sense to exclude Human Fighter when you've given it to Dwarf, but Human gets No class ability benefit from this token. There's a logic error happening in my mind. Why not make Rare Bead(s) for DF, Rogue, Druid (when polymorphed), and UR for all? Make the Rare ones Completion and/or Treasure tokens