I cannot think of a better place in the County to get fantastic views of Swifts that the middle reaches of the Western Cleddau. Yesterday evening at St Catherine's bridge (near Camrose) there were 30-40, feeding intensively, and almost silently, for several hours, until replaced by bats as the light faded. With a good hatch of assorted flies, the Swifts were flying low, seldom straying more than a few metres from the line of the river, and often coming past my ears from behind; rather disconcerting!
Other birds of note: Kingfishers, Grey and Pied Wagtails, and the regular calls of young Tawney Owls. The stretch of the river downstream from the bridge is part of the Cleddau Trail, and so has good access.