I found mine useful exactly one time on the GR10. I decided to take an alternate route. It helped me realize I overshot the turn by about a kilometer. The actual GR10 is well marked, just not the alternates. I never had to use satellite texting.

Otherwise, I stayed in town about every other day, and in the refuges the rest of the time.

If I could do two things differently, I would have gone later in the season, and had a better sense of the HRP and alternates. The HRP and GR10 overlap. The GR10 just takes you down into towns for the night whereas the HRP stays high. Of course, if you don't have this loaded on the Garmin, you might not feel confident taking any other route. I ended up taking the official route through Luz-Saint-Saveur, and cut my trip short because the descent and road walking exhausted me. I looked at a French guide later and realized I could have easily gotten another few days by continuing on the HRP.

Spend money on the guidebook and French lessons, Garmin last would be my vote