One of the key things I needed was an easily attachable mechanical rope grab that was compatible with 16mm lines.
After hunting around for a while I stumbled across this ISC rope grab.
Not necessarily what I initially had in mind but it is compatible with 14-16mm lines (and will actually fit our 19mm bull rope in as well, although not recommended)
This model comes with a push pin. Basically by pushing the small silver pin in the middle of the red ring you can see, the pin then slides out releasing the cam
Not something that can be done one handed but is quick enough and hopefully will work pretty well for what i have in mind for it.
I quite like the simplicity of this device, no springs or small parts to go wrong and the only 2 moving pieces are attached via small wires. It has a very solid feel to it and I have no doubt it would take a lot of abuse before showing any signs of ware. Now I just need a few more bits and I'll hopefully have something a bit more interesting to share...