First things first, I haven't played a game with biests yet, so this is just a preconception.
The level 2 biest class seems hardly worth it. You pay double the base species cost up front for an extra attack. With biests already having a base cost this gets expensive quickly. Secondly they don't have acced to wildling which was discussed in another thread as being intentional. They can buy a characteristic increase for 10 points. So compared to the level 1 class you get: +1 attack, +1 max properties, +1 max class traits. You pay: +1x species cost, +6 (poinst difference) for a characteristic increase
And also the option to pay 4 points for a situational bonus.
Again, I am not in a position to judge how good or bad it actually is, but it feels like you are paying a hefty premium for a fairly meager benefit in the form of room to grow. Which, in terms of traits will only make the model more expensive. If I can field almost 2 level 1 models for each level 2 model, why bother with them? Again, this is ofcourse wildly dependent on species and faction traits. But for kingdoms with a high base cost, like avian, if you want to even slightly customize your species with some traits, the cost of higher level classes skyrockets, while you aren't getting much in terms of staying or hitting power in return.