The last time I used Rust for any sort of project was two years ago, and the code size concerns were one of the first things I thought about when contemplating

The last time I used Rust for any sort of project was two years ago, and the code size concerns were one of the first things I thought about when contemplating writing for embedded targets in Rust. Executable sizes were really bad, especially at -O1 optimization levels, but I haven't really seen much of a problem in practice today so maybe they fixed it. From a performance and memory efficiency standpoint, Rust is on par with the C/C++ projects I've worked with. Some things slightly worse, some things slightly better, but nothing egregious in either direction. I will say that the coroutine-based async facilities in Rust's embedded-hal and embassy-rs projects make task-based concurrency so easy to do with bare-metal code that there isn't much need to use an RTOS in many of the situations that a C/C++ project could do. That sort of OS-less concurrency is no doubt possible in C, but I shudder to think what it would look like.