My vouch wouldn't probably mean much, but yandex are by and large not-evil guys. They can be forced to abide the law, but I believe they haven't willfully done anything really unethical yet. Unfortunately, yandex search is inferior to google for English queries, which diminishes their usefulness a lot.
I tend to trust almost all techies by default, but their government, not so much. The same thing applies to the US, though, although at least in the US there's enough precedent from pre-2001 or pre-1990s to restrain the government slightly. Russia and China don't have the extended period of relative legal sanity the US had from ~1781 to sometime in the 1900s, or common law tradition from England from 1300 onward.
