The worker has a chassis that's not too surprising for an outsider. Boosts to a few physical skills, immunity to some energy types/conditions and resistance to others, an alignment subtype and a single (weak) natural attack.
Then there's a formian's supernatural abilities, which are sadly better suited to a monster than a PC. Hive Mind will basically only be useful in a 50-mile radius on a single outer plane (and even then it's not too great) and Cure Serious Wounds requires seven other workers. I guess a party of four workers that all pick Improved Familiar (Formian Worker) could pull it off, but that's an awful amount of resources to get free healing. Make Whole is much the same, though I guess only two more workers are somewhat easier to gather.
To make things worse, formians cannot speak or wield weapons (a fact explicitly spelled out in their description), which means casters have to pay a feat tax and martials need to spend money on Mouthpick stuff. I guess you could play a warlock, but that means... well, being a warlock.
All things considered, I think +1 LA is enough. While a worker may have several strengths not easily obtainable at ECL 2, its weaknesses make actually contributing to a party hard.