These munitions were used extensively,particularly on the Eastern Fron. They were also dropped in considerable numbers on Britain. I'd have to check if that particular system for dropping them was much used but as that Luftwaffen Dienstvorschriften for the E and F was published in 1941 I suspect it was. The AB containers (abwurfbehalter) were much more practical and could be used with the standard ETC racks. They were also made of wood,cheap and non strategic
Why were the "butterfly" bombs temperamental? Once dropped and opened (armed) they were very sensitive but I've not read of any handling problems during loading. They really crammed them in to those containers.