Paul Barnes, writing for Commercial Type:
The roots of Darby lie in the British tradition of lettering and typefounding that began to flower in the middle of the eighteenth century. Behind the contemporary bodies, one can see the structural qualities of the three major type founders of this period; John Baskerville of Birmingham, Joseph Fry of Bristol and Alexander Wilson of Glasgow. The high body of the bowl of the a, the open g, and the bow in the £ are all typical of the style.
Love it when type designers talk about the formal inspiration behind their typefaces, because it offers us ways of talking about the type, and hints at examples we might study. This makes me want to look over Baskerville entries at Fonts In Use, for example.
Paul adds, about Darby Sans:
We feel that it may be our best screen typeface to date.