The extra options along the coast are a quality alternative to the roads that get you to Figueras. However you may be swayed by the somewhat confusingly created signs for the albergue in Figueras. They are full of arrows and say Camino del Norte and their primary function is to get you to the albergue.
The border between Asturias and Galicia is spanned by the Puente de Santos. This bridge is the major highway across the Río de Ribadeo below and you have to choose which side you want to cross on in Figueras. The only differences between the two are the views and the egress on the other side of the bridge. The north side of the bridge has better views of the sea, and it delivers you closer to the municipal albergue which itself is north of the bridge.
Most but not all of the routes which got you to Figueras will lead you to the roundabout on the south side of the A-8, and arrows indicated the way to the bridge. To get to the other side means ignoring these arrows and passing under the A-8 to the sister roundabout on the other side. There you will find more arrows directing you up the old ramp and to the crossing.
At the other end:
From the north side, the camino veers away from the A-8 and downhill. When it gets to the road it turns sharply right to go back towards the river. At the river the albergue is a left-hand turn, and the city and camino are a right-hand turn to pass under the bridge you just crossed.
From the south side: This way is a bit trickier and essentially forces you to get back to the north side of the bridge temporarily. At the end of the bridge the path veers away and meets the road. Turn right here to go under the A-8, turning right again and back towards the river once past it. Here you rejoin the northern options and at the next junction the albergue is to your left and the city and camino are a right-hand turn to pass under the bridge again.