i would say the mice and rats are better for them because they are a natural food source for snakes,and you dont really know whats in those sausage things and weather they might need suplements to go with them because they might not have all the nutrients and vitamins in them,as mice and rats do have those anyway.i would stick to mice and rats to be safe
i reckon if mice are a real no no. rough green snakes would be fascinating. they are incredibly stealthy predators and sway as if to mimic a branch blowing in the wind.
i'd get them myself but i can't stand horrible things like crickets and meal worms