We have 2.
An 11 year old JRT and an 8 year old Parson. There is a difference. Not all of them are actual AKC Parson's like someone said earlier. There are several different "types" of JRT's. Only the Parson Russell Terrior is recognized and competes ib dog shows.
There are short haired, long haired, broken coat, short-legged (shorties), tall ones, Parson's, etc. The variety is the reason they were not recognized by the until AKC 9-10 years ago. I guess the AKC chose one and they went with the "Parson"
We love them they are definitely unique and require a special kind of "master".
They are highly intelligent but have a mind of their own and can be stubborn. If you have ever had a toddler, it is a very similar experience.
We kep both in our apartment when we lived in Hoboken. But they love our yard.
I would really call them hyper, I'd call them "easily exciteable".
They lie around the house and nap most of the day but when anyone comes over they get all wound up.
That's why most people who have visited people with JRT's always say they are hyper. Because they saved all that energy for the guests.
There are 5 in my family. We have 2, my mother has 2, and my in-laws have 1.
If you are looking for a mellow low maintenance dog you should probably look at other breeds. As long as you know what you are signing up for, they are amazing, smart, loyal companions. They are "crazy" in a good way IMO.