I am not generally a fan of Sustans' cycle routes. Although dedicated cycle routes are a good idea and work well elsewhere in Europe I find that in the UK the enthusiasm to provide them runs ahead of the ability to do so. This often leads to poorly-surfaced and badly-maintained routes, inconsistant or non-existant signage and it's usually easy to spot where the money ran out as the route just stops, with no indication as to how one reaches one's destination other than an "End of Route" sign!
But the Bath to Bristol cycle path is different: well-surfaced and signed and part of a joined-up network that it was a pleasure to cycle on to avoid the heavy traffic on the A4 and the Bristol ring road.
We made such good progress that we were able to take lunch at the Aust motorway services that overlook the estuary (or at least if you take the trouble to walk from the car park, they do).