I've encountered nipples without the handy slot on the back, pain in the ass. Thankfully seems to be the cheapy steel wheeled bikes that have this.

I have a set of Performance branded spoke wrenches and I've never been very satisfied with their fit, never feels very snug. Similar wrenches have felt the same too, doesn't feel like any precision to it, just loose feeling, easy to round off a nipple if you aren't careful