The Irish Staffordshire Terrier or perhaps more correctly the Irish Bull Terrier is essentially the original Hinks Bull Terrier crossed with pre war Staffordshire Bull Terriers. It is not an American Pit Bull Terrier or American Staffordshire Terrier as it is a distinctly different line albeit still a descendent of the original English Bull Dogge and Fox Terrier lines.
The animal is lighter and smaller than its American cousin with a different skull more aptly described as a coal bucket shape rather than the APBT brick shaped head. Normally the male weighs less than 60 pounds and stand no more than 19 inches at the shoulder with the female somewhat finer and smaller.
The dogs are simply a more athletic version of the Staffordshire Bull Terrier; in fact they are the original blueprint rather than the dog show exhibitors corrupted model. They similarly to the Victorian Bulldog consequently do not have the same issues with running in the heat etc as their modern counterparts.
However they share similar mental characteristics to the American version but better at killing vermin such as rats as they are quicker and more agile. Technically they are not banned under the Dangerous Dogs Act in the same way as American Bulldogs are not illegal to own in the UK.
They are a utilitarian dog able to carry out most activities with the correct training but do have a high prey drive therefore should not be owned by anyone not versed in basic dog psychology.