My shooting board is consistently accurate, or at least as accurate one can be with a try square and the human eye.
The key to making a consistently square case is in stock prep. Make it flat, make it square, make opposite pieces the same length. Squaring a piece is fairly easy with or without a shooting board. Making two or more pieces the same length is a simple task for a shooting board. Removing excess length of a "skosh" or less is fast work with little noise of an electric motor. Maybe even faster than firing up the table saw (if I had one).
I don't like gaps either:
Attachment 512871
This was cut on a miter box by hand with a thin blade saw. The "saw fuzz" was removed on a shooting board. I like the wood grain to line up as much as possible on the vertical face of the miter. I guess on an electric power saw this would require switching to a thinner blade.
I have made a few of these small cabinets, so I am not sure if this one was dead on or required a little adjustment to come together without creating a gap. Small adjustments of a degree or less are fairly easy to do by hand & eye.
I have made simple, permanent accessories to shoot angles of as little as 2-3º off of square up to 22-1/2º & 45º. There have also been a few others for one off projects.
jtk