im sure there'd be some excellent workers in there, but whether they would pass that on i don't know.
people line breed for number of reasons size, temperament, working style, nose, coat etc etc - it being "a good worker" is a given - thats the minimum it has to be.
the line breeding hopefully fixes the features you want.
Glyn and DD have obviously had a lot of good terriers, but i'm sure there will be subtle little differences in what they want from the perfect terrier.