I have to agree. It's one thing to say, we're going to find and test your limits. It's another thing to do so without foreknowledge on the sub's part that this is the purpose of the play.

To "teach" a sub that it's okay to use a safeword merely "by example" is, I believe, over the top.

Too many subs are totally invested in their dom's happiness and will suffer in silence far beyond the limits of their own pleasure. The purpose of D/s play, or at least my purpose, is mutual pleasure. If it's not mutual, then why bother searching for a compatible sub/dom?