Oh easy-to-rate monsters without complicated abilities, how I've missed you.
Digesters have 8 magical beast RHD. That's not horrible, but they don't get a lot for it either. Moderately high physical stats, average wisdom and charisma, abysmal intelligence. Its speed is surprisingly high, but that matters little.
The real problem with digesters? Their horrible offensive abilities. Acid Spray is completely outclassed as an area attack (a semi-optimized Dragonfire Adept can do better), and the single-target version is little better (not to mention the horrible range). In the 1d4 rounds in which this ability recharges, digesters can, at most, make a single claw attack per round.
To put it simply: digesters suck. -0 LA.