My overall conclusion is that this is a fabulous walk. This is the ultimate alternative route on the Camino del Norte, staying on the coast after Ribadeo and joining the Camino Ingles in Ferrol for those wishing to walk to Santiago.
The views are spectacular, the signage excellent, at least whilst still on the Ruta Natural del Cantábrico, a little less so thereafter, and many of the towns, whilst not beautiful, as they are on Italy’s Via della Costa, they give a real insight into life along this part of the Galician coast.
The paths are also generally good, but there is a fair bit of walking on roads and stone paths, which is hard on the feet, and probably the main downside. On saying that, my guess would be that there was less road walking than on the Norte (but that is only a guess). The elevation profile per kilometer is similar to the Norte between Santander and Ribedeo. Between Ribadeo and A Coruna I had planned to walk 263km with an elevation profile of 6.700m, versus 375km and 8.600m between Santander and Ribadeo.
This is a lonely walk. I did not meet a single other through walker between Ribadeo and Ferrol. I met some, not many, day or pleasure walkers. So you need to be prepared for this if you walk alone and one of the reasons you walk is to meet other people.
The other challenge for many is finding budget lodgings. I don’t walk on a budget and I walked outside high season, so I didn’t have any problems finding places to stay. I stayed in small pensions, and a couple of nice hotels, as my choice of places to stay had more to do with a) being on the trail b) how long I plan to walk – I normally walk 30-35kms.
I book everything in advance, partly as I walk alone and it is good to have some fix points for my wife’s peace of mind, and also I just can’t be bothered wasting energy thinking about where I will be staying tonight and if there is room. Given I can consistently walk 30-40kms, I have so far not found pre-booking to be a problem. On some of the more off beat walks, like this, Lighthouse Way and the Fisherman’s Trail, I think pre-booking is often (not always) necessary.
So where did I stay, and my comments about where I could/should have stayed.
Day 1: Rinlo (before the Cathedral National monument) I walked from Tapia. Stayed at Mi Norte, which was 2 kilometers off track. In retrospect I should have tried to find somewhere in San Miguel, just after the monument e.g. Hotel Playa de Las Catedrales. (Mi Norte is an excellent hotel, but not close to very much)
Day 2: Foz – Isla Nova Hotel (there are other places to stay)
Day 3: San Cibrao – Hostel Buenavista (only place to stay I think)
Day 4: Celeiro – Hotel Boa Vista. In retrospect I would try and find a hotel in Vivero or Covas. Boa Vista was good value (for me) given they have an excellent restaurant, and I was hungry 
Day 5: O Vicedo – Pension Galatea
Day 6: Ortigueira – Casa Gil – was on the track, but 2km from town. I retrospect would look for something in town. I recall that there is a hostel.
Day 7: San Andrés de Teixido – Casa Rural de San Andrés de Teixido. I stayed off season so price was reasonable, but a really nice place to stay.
Day 8: Valdovino – A Torre do Lago – again chosen because it was on the trail, but 3kms after the town. I would see if there is anything in the town itself. There were many surfers, so I would think that there is something.
Day 9: Pontedeume – on the Ingles, at least one hostel in town
A couple of final thoughts.
The walk from Epasante to A Ponte de Mera is not super interesting and I have read that some take the train on this stretch. This gives a couple of options a) walk O Vicedo to Espasante and take the early afternoon train to A Ponte de Mera and walk to San Andres and stay there or b) take the next morning train to A Ponte de Mera and walk to Cedeira via San Andreas.
If I was doing this again I would follow the coast after climbing out of San Andres and Cedeira and again from Valdovino to Ferrol. On the trails I was following, both these stretches are inland, primarily on road and not super interesting. Cedeira to Valdovino already follows the estuary and coast, so you can just follow the trail on that stretch. Bottom line, I would walk San Andres – Cedeira, and Cedeira to Ferrol, following tracks along the coast.
So, a highly recommended walk, and whilst the Camino del Norte had some fabulous walks along the coast, I would certainly choose the Cantábrico if I had to choose.