My understanding from Aria Beingessner's and some other writings is that unsafe{} rust is significantly harder to get right in "non-trivial cases" than C, because the semantics are more complex and less specified.
This is definitely true right now, but I don't think it will always be the case.
Unsafe Rust is currently extremely underspecified and underdocumented, but it's designed to be far more specifiable than C. For example: aliasing rules. When and how you're allowed to alias references in unsafe code is not at all documented and under much active discussion; whereas in C pointer aliasing rules are well defined but also completely insane (casting pointers to a different type in order to reinterpret the bytes of an object is often UB even in completely innocuous cases).
Once Rust's memory model is fully specified and written down, unsafe Rust is trying to go for something much simpler, more teachable, and with less footguns than C.
It's hard to compare. Rust has stricter requirements than C, but looser requirements don't mean easier: ever bit shifted by a variable amount? Hope you never relied on shifting "entirely" out of a variable zeroing it.
