Currently there appears to be no way to tell from the AH (or other in-game sources), whether a companion is Invoker, Fighter, Beast etc. Also no way to tell if their bonus ability goes into your Offense, Defense or Utility slots.
Fairly key info that is needed when trying to acquire new companions, I would think.
They could address this in the short term by adding or repurposing some of the search category slots in the Auction interface. Where we put in Class or Enchantment type, for instance, could become Category (Fighter, Invoker etc) and Companion type (Offense, Defense, Utility).
Or they could add two new dropdowns for it, like the 'Stats' dropdown that appears when searching for some types of equipment. Either way, when we need to fill a Defense slot with a new Mystical companion, there is currently no way to do so other than heading out of game to player made lists like Rainiers 'Mod 16 Pocket Wiki' and searching through the list one by one til you find a match, then tabbing back to the game and searching the AH to see the prices on that one, then tabbing back out to find the next one, etc.https://docs.google.com/spreadsheets/d/1fP_cUugHdsObvQDzLFijGA-mVm_qLmSy0MI62aTLkDM/htmlview?usp=sharing&sle=true#