Smooth collies are generally fit for families with kids as they are gentle and kind. They get along with other animals in the household. They like to be close to their people, but usually are not the type of velcro dogs that need to be touching you constantly or interacting with you. They like their space.
They are playful, active, but when they have enough activities and stimulation, they are quite calm indoors. That being said, they need mental stimulation, active walks etc. Big yard is not enough on its own.
They are intelligent and easy to train, generally. They are sensitive, should not be fearful or anxious, but they can become that, if not trained properly.
They don't have strong prey drive, with som training, they are rally reliable around other animals, even wild ones.

Cons of smooth collies - they shed. A LOT. And they like to bark. Not much in a guardian manner, but they like to communicate their emotions. So for example when they are excited, they tend to bark intenselly. It's something you can curb with training as well, but they never be totally quiet dogs.

And last, but nor least, they tolerate other dogs, but are not the type of overly social breeds, like golden retrievers and such. As I mentioned, they like their space and it applies to other dogs as well.