Hello Jason,
I might run into you guys! I am also planning to start the Norte/Primitivo from Bilbao on May 21 or 22, we'll see. At any rate to contribute my 2 cents worth to your question. I've done my research and I've selected the following for my Caminos: In my humble opinion the best one it's
Gronze.com
(a Spanish website with tons of FREE information on all the Caminos);
Buen Camino App by Editorial Buen Camino cost me $5.49 for the Norte and the Primitivo it's the same $5.49;
Camino Assist by TDINET APPS, also $5.49 but this one includes the Norte, Primitivo and Ingles for one price.
MI CAMINO APP, has the Norte and Primitivo, a ton of info and it appears to be FREE !
.
There are others but I wasn't crazy about them, you might want to look at the them and evaluate them for your needs:
CAMINO DE SANTIAGO de Eroski and MUNDICAMINO. Now the benefit of all the aforementioned, it's that they will all fit in your smarphone and will not add additional weight to your backpacks, that's a big plus. I realized that we all have different needs in whatever we do so I gave you as much variety as possible so that you can make a semi-educated decision on your selection. Good luck, Buen Camino and be on the lookout for a grey-haired peregrino walking the Norte/Primitivo, you will probably pass me.
Take care,
Ignacio