At least I think so. And I have found a good job for Nico.
First, you should know that rat terriers were bred to be a poor man's all purpose dog. They were supposed to be excellent family pets, although their tolerance for children is not limitless. They are good at killing small mammals- think rats. And they are supposed to be good at herding.
Nico has shown an amazing patience for family life. He can get a potty mouth when he feels he is being handled too much, but he has not offered to bite anyone in retaliation. He DOES nip hands when he's excited, but never with the intention to hurt. He mostly wants to sit in a lap when he's inside, so much so that one could think he's a couch potato. However, if anyone is going outside, he will beat them through the door and follow them wherever they are going. He is the perfect companion dog.
As for killing small mammals, I believe I've reported before that he takes care of any moles that happen into our yard. The cats tend to kill the mice and shrews. Fortunately, I have no idea if he would kill a rat, but I like to think he would.
I have seen many signs that he is willing to herd, but it has often been a frustration rather than a help. He gets so excited when we're moving chickens around that he will run them every which way. I know if I could train him, I could teach him to drive the chickens the direction I want. With the cows, he has been a little help. The cows are not afraid of him, but if he darts in at just the right moment, he can push them down a lane they had been balky to move along.
Last summer, we realized that he is much better than we are at chasing the chickens out of the barn-like structure where we store hay. I worried sometimes that he might try to get a mouthful of chicken, but he never did. And the more often he is called on to do the task and given a command to stop doing it, the calmer he gets executing the herding of chickens. With the thaw, the chickens are now ranging over the entire property. We want this for the most part. However, I do not want them in the yard or in any of the gardens. The flex-net we're using around the garden was pushed down in a couple of places and I could not put it back up until the ground thawed.
He is quite smart and seems pretty able to figure out what we mean when we say, "Get the chickens out of the garden!" Then, he's so delighted with himself. Also, the more he often chases the chickens out of the yard, the less likely the chickens are to keep coming in the yard, as they have many other places to go. Interestingly, the result is not that Nico then chases the chickens every time he sees them; he really seems to grok that he is only to chase them when we say so. He seems quite pleased to be called on for this job, and a working dog is less likely to give you other trouble.