I use them all the time on magpies/crows usually off a known perching area at a measured 44 metres and they always drop to the shot, never had a runner yet. My understanding is that the cartridge was developed by RWS for basement target shooting at less than 10 metres range.
They cost strangely 8 Euros a pack in Germany and only 6 Euros a pack in Austria.
Never tried the CCIs though.
Ive been using CB longs on and off for a while and had okish accuracy with a fair few flyers, taken a few rabbits round the farm yard. Just heard about the z lang range a wondered what peoples views are
I've found rws z-langs to be much more accurate than cci CB longs. They are faster though, I chrono'd them at around 880fps if I remember right. All in all though, a good reduced velocity round. The best of its kind imo.