The API side of this library is pretty good. I've generally avoided it due to the compile time, and preferred rapidjson due to both better performance and compile time if I wanted a C++ API, or cJSON if a C API is fine and I really just want an extremely low compile time (lately I've been playing with a live coding C++ context for a game engine, as a side project, I use cJSON there; rapidjson on main project though) (cJSON's tradeoff is it sticks with a single global allocator that you can only customize in one location, and also seems to perf slightly lower on parse).

The cJSON's C API or rapidjson's somewhat less ergonomic API has felt fine because I usually have read / write be reflective and don't write that much manual JSON code.

Specifically for the case where compile time doesn't matter and I need expressive JSON object mutation in C++ (or some tradeoff thereof), I think this library seems good.

Another big feature (which I feel like it could be louder about -- it really is a big one!) is that you can also generate binary data in a bunch of formats (BSON, CBOR, MessagePack and UJBJSON) that have a node structure similar to JSON's -- from the same in-memory instances of this library's data type. That sort of thing is something I've desired for various reasons (smaller file types with potentially better network send time for asynchronous sending / downloads (for real-time multiplayer you still basically want to encode to something that doesn't embed field string names)). I do think I may end up doing it at one layer above in the engine level and just have a different backend other than cJSON etc. too though...