You may have found there are a few different ones available. I have the one piece cast aluminum type which fastens to the window pin with a set screw and plate over the latch. It works well and I've never had any problems even over the rail road tracks in my route. Mind you, the tempered glass will take quite a beating anyway and it floats a little in the hinges (up off the rubber). They also suggest you not run with the top out and the spacer in place since the air flow can reverse and suck exhaust into the cabin.

I have a hatch vent as well.  It is the one that attaches to the glass latch with a twist with the spacer next to it.
It works GREAT.  It allows the air to flow throught the interior and keeps the car really cool.  Plus I can hear my
"Magna-flows" through the back   :) 
I have railroad tracks that I have to drive over in town but have had no issues.  Of course I take my time when
I go over the tracks.

Love it, worth the $$

Regards,

Darryl
96 CE