Himself is on a mission at the moment to standardise, as far as possible, all our couplings.
This has gone so far as to fit brass Greenwich couplings to the lead and tail waggons of our slate train where they couple up to the locomotives.
Previously these were fitted with chunky plastic BEMO couplings which for a long while were the standard in OO9.
The most vital thing with couplings in any scale, but especially this one, is that they are aligned properly for height with one another and you can see in the picture how we use a little jig knocked up out of styrene to set the height of the bottom of the coupling face.
The advantage that the Greenwich design has over all overs is that because the shaft is made of brass it is easily bent either upwards or downwards to make fine adjustments - the key thing is to make sure it is fixed very firmly to the model, otherwise you will pull it off when you go to bend it.