The straight-down-tail-slide is only a minor part of the problem. That condition is bad, but it rarely happens simply because you have to try to slide tail first to get into it.
What is the main issue is that you can be flying along in a perfectly normal part of the flight envelope and for no reason your tail will slide out from under you like you lost your stabs and THEN put you into the tail slide.
My distinction is not that the tail slide is hard to get out of, it's that you shouldn't get INTO IT in the first place in most times it's happened to me. Basic, controlled, well above stall speed maneuvers, and for no reason (even with moderate inputs, NOT forcing it to do bad things) your tail will just whip under and you're flying backwards.