Most approaches, I assume, will leverage conditional compilation: When (deterministic simulation) testing, use the deterministic async runtime. Otherwise, use the default runtime. That means there's no (runtime) overhead at the cost of increased complexity.

I'm using DST in a personal project. My biggest issue is that significant parts of the ecosystem either require or prefer your runtime to be tokio. To deal with that, I re-implemented most of tokio's API on top of my DST runtime. Running my DST tests involves patching dependencies which can get messy.