From personal experience, it's not that bad. C++ is "Java plus you need to worry about these other things", and it pays off in power and speed. They're not so similar in safety/scope terms, but the structure and design have enough in common that you get plenty of spare brainpower to worry about managing C++.

It was, for instance, a way more natural transition than "Java and C++ to OCaml". Less educational, but as usual that trades against easy.