> At the cost of making the use of the resulting heap significantly slower and larger than if you just wrote the thing in Java to begin with, though!

Lower throughput, probably. But it introduces constant latency. It has some advantages over doing it in Java:

* You're never going to get latency spikes by adding a counter to each allocation slot.

* If you really want to, you can disable them in release builds and still not give up memory-safety, although you might get logical use-after-frees.

* You don't need to use such "compromises" for literally everything, just where it's needed.

> It starts from a marketing position of "Safety With No Compromises"

I haven't seen that marketing, but if it exists, sure, it's misleading. Yes, you have to compromise. But in my opinion, the compromises that Rust lets you make are meaningfully different from the compromises in other mainstream languages. Sometimes better, sometimes worse. Probably worse for most applications than a GC language, tbh.