Product review (5 stars): Perfect replacement!
It's perfect!  It's the same as the one that came with our GD (Evolution Septic Assist).  Yes the "initial" opening is small - but it helps prevent unwanted items from slipping into the GD and it prevents "backsplash" from the grinding going on in the disposal chamber when turned on.

It installs easily and is easily removed for cleaning (yes, it definitely needs to be cleaned occasionally!)

To get food into the GD chamber, simply push it if it's too big to slip through - you don't have to push it all the way into the chamber.  When the food is being pushed in, the baffle easily opens up - it expands to a much larger hole - so the food goes in but the utensil used to push does not (use a utensil, not your hand!)  If you're concerned about safety, then push the stuff down b/f you turn it on (or, better yet, get a Batch disposal - but that's a different GD.)

Regarding water drainage - if you turn on the disposal it quickly sucks all the water out.  It isn't that bad, though, water does drain pretty well when the disposal chamber is empty.