Hello Vincent.
What are your requirements? I would have thought between Apple, google, and baidu maps on the iPhone, you’d have everything you need.
I thought Baidu and Google even has turn-by-turn functionality in China on iPhone? (they do on android so I guess on iOS too)
I found that as you go deeper into the countryside these maps services can have different levels of detail depending on where you are and what you need. so between the 3 they are a accurate as you can possibly buy. Apple (allegedly) has great/the best maps for smaller towns in China outside of the big cities.
the things that sometimes catch me out are:
-ending up somewhere without network to access the map data. you will likely only get this on china Unicom (and less so everyday) unless you go far west into far Tibetan areas. You can mitigate this by downloading/caching maps of the area you’ll go before you leave.
-running out of battery; get one of those portable battery pack things.
I also explore quite allot out of Chengdu using my phone. if you’ve got any other questions please ask.