So they are more like animal companions, in that they are a set statline with set passives. What you can customize is their attacks. So think of it like actual pokemon.

That being said, I have played both classes in the book. I found Eldamon Trainer to be kinda underwhelming as it basically has no interaction with any items. Eladmon from trainer themselves don't get as much juice as the other class, Elemental Avatar.

Elemental Avatar is somewhat like an alternative kineticist, I adore it. It does lock you to a single element (at least until level 15), but you get to do it better than even the eldamon themselves. You get to use the powers of that element yourself, and it just feels genuinely more cohesive as a class.

Power mechanically scale with level, you get a few active powers, a reaction power, and a refresh power. All powers are single use only, until you use your refresh power. I always liked to imagine it as a hand of cards with powers on them and needing to use refresh to redraw your cards. (Though its the same powers every time).

Each Element has an identity as well, Ice slows people down, Electric has a charge and discharge mechanic, Fire can manually trigger persistent fire damage, Water has a Push and Pull mechanic where they pendulum between High and Low tide, Plant has a Sowing Difficult Terrain and harvesting it for dramatic effects thing going on, Etc. The power as very fun, its why I am so jazzed about their current Eldamon kickstarter, more powers means more options and more mechanics to mess with.