I have built about six or so beds and have tried a couple of different
attachment hardware fittings and always come back to the traditional bed
bolts . I usually get mine from horton brasses ,cromwell conn. Beware of the
barrel type nuts if overtightened they tend to apply pressure radially on
the wood which in turn can cause the wood to split . The plane flat nuts
distribute the load linearly. mjh

I finished a queen sized bed last year, and I first tried the bed rail
connectors like those you mentioned from Woodcraft (mine were from
Rockler). I used some on a different project first, and found they
didn't fit as closely as I'd like - I could never get them to pull
themselves tight, as they're supposed to. I tried playing with
mortise depth and shims and even filing down the "hooks", but I could
never get a nice tight connection between the two pieces - YMMV. I
wasn't too impressed overall.
So I ended up making basically my own version of a "bed bolt" - LV and
Woodcraft have versions, as linked in previous replies. I didn't want
the fancy end caps for my mission style bed, so I used pyramidal wood
door pulls cut to a press fit into the countersinks. I also didn't
like the idea of a round barrel nut, for the reasons mjh mentioned
above, so I mortised a flat-ended opening in the side rail, and used a
3/8" bolt through the post, with a filed-down washer and nut inside
the side rail. I also put in a couple 3/4" dowels to take most of the
weight, so the bolt wouldn't have to take any weight, and could be
used primarily to tighten the connection. I'm sure it's
overengineered, but it was sort of fun and the thing hasn't even
wiggled in a year (despite my best efforts...)
Good luck,
Andy