I'm not saying people can't want this, but retermination of a cable won't cost much more and is a better solution than this 4.4mm to 2.5mm adapter, albeit potentially slower (though Drop is not known for speedy delivery).
As I've said before 2.5mm is frail, so having the plug body not press directly against the source is bad design. The collar prevents the adapter from having the broadest possible base. I'll say one more time: the need for 4.4mm to 2.5mm is rare, and if you have this need, this is not the best solution. Best solution is reterminate your cable, 2nd best is an adapter that is not of the direct connect variety (that is, wire between male and female connectors). If ddHifi wants to make a 4.4mm to 2.5mm adapter, they should ditch the collar on the 2.5mm plug and give a broader base. I also have it on good authority from a cable manufacturer that right angle connections break more, because they rotate and leverage breaks the connector.