At the moment I cant really throw any further than 100y as it is not at all optimised yet, but I have made some interesting discoveries. It feels very strange compared to a sling because the hand has to really lag behind and then lots of forearm and wrist muscles are used to flick it forward to release. It is shorter than a cesta, but it is lighter at 160g in weight. I think accuracy is certainly possible, but a lot of practice is needed to do so with different weight stones. I have also found that if an elongated stone is placed in line with with the spoon, it will actually rifle the stone somewhat (not as well as a sling where perfect stabilisation is possible).
When I switched back to a sling it instantly occurred to me how I was able to generate velocity with much less effort.
In all, I'd like to try and optimise (length, shape, etc)it and see if I could get better velocities.
Although if  ~50m/s with a ~100g stone using a light 18" sling is possible, then I think 70m/s (Jai Alai speeds) would certainly be possible with the same stone and a 36" sling (and I think would be more effortless).

This forum always amazes me with how little it takes to make something you can throw rocks with 90m+.

Also I would kill to have pebbles like that just laying around here. I really have to give a visit to the closes proper river(which is 10km away)