My original Big Whale tufnol stand-up block and cleat for the main (on a DS1) has an upward release (pulling up releases).
My take: it's nearly always possible to pull more upward, so you can never get stuck with the sheet cleated. The angle of the fitting is such that positive cleating is possible from all seating positions (in other words, a pull that clears the rail plus knees of the operator is low enough to affect cleating).
I've sailed on a DSII with original downward release and had the main cleat itself constantly when going upwind in gusty winds, where I was very interested in
not having the d****n thing cleat itself. I really, really hated that
.
If you fit a ratchet block, there's even less need for the main to be cleated all the time, so the utility of "auto cleating" is even more marginal -- but to each his own.