Open seating on inter-island flights is the default policy for both Hawaiian and Aloha. It's almost a necessity since they have to turn around quickly, and often there are quite a few stand-byes from later flights. The flights themselves are very short anyway, all under 1 hour.

As for Mainland service, my limited experience is that their seat pitch is indeed tighter than AA's in econ, but (at least for the few times I flew on HA), the FA's were generally much more cheerful and helpful, and they got to wear regular FA uniforms rather than those silly imitation muumuus.