Cockroach trusts the MaxOffset, and if your clocks don't live up to the promise, you might get some stale reads. By the way, Spanner breaks in the same way if their clock offset (via their TrueTime API) fails them. But Spanner has to wait out the MaxOffset on every commit, we don't - so we get away with having it high enough for off-the-shelf clock synchronization and save you the atomic clocks, at similar guarantees. That's a very good deal. If you happen to have atomic clocks around and you have strong guarantees on your uncertainty like Spanner does, you get linearizability at the same price.

For a more in-depth explanation of the above, see https://gist.github.com/tschottdorf/57bcccc379b151456044.