I have not used either for cars but I have tried both for driving bicycles. The thing with open street map is that they have a lot more of the small streets that bikes can go on but cars can’t. In my experience google maps usually wants me to drive my bike right on some huge multi-lane car road for 3 hours and totally ignores the bike path right next to it. When I went on a 1 month bicycling trip I tried both but found that OSMAnd had vastly better suited roads. Some of the tiniest tiny roads it sent me on were some of the most memorable of the whole journey. Sometimes the path in OSMAnd will just be a dirt path half a meter wide and I love that. I thought many times who on earth even added all these roads! I’m so thankful for every local nerd who added every single dirt road in his neighborhood on there. Simply amazing sometimes. But yeah it doesn’t work at all if you don’t download the map that’s true. Also I really can’t answer for navigating by car.
You are supposed to never have any other god before the Christian god at any moment. That means that if you pray to the Christian god every day of the year except for one day where you suddenly pray to another. Then during that day you put another god before the Christian god. Think of it like cheating in a relationship. Even if you are exclusive to your partner 99% of the time that 1% still counts as cheating.