I am told that this will help keep the concrete from splattering durring the poor. Is that true? Z boom 1300 Rpn full hose with tree nails at #4 pumping volume.

Very dangerous! Rock or fin jam hit nail plugs briefly bends nail violent hosewhip million dollar lawsuit. 

I use that trick when topping curbs or pour in place walls. We're talking sloooooooow pump speed. Any other speed, no way. 

The EXCALIBUR concrete brake from Putzmeister worked the same way, and they passed it safe for everyday use, its essentially the same principle, so there shouldn't be a problem. Does it work? Yes. But the problem here is the hoseman is always dealing with a FULL 5" hose which (s)he may not be very pleased about long term.

Bit like this one. While I was looking for this pin pour picture i stumbled across some other 'interesting' device

Anybody who used the PIN Pour from Putzmeister should by now have a view of "our Putzmeister friends behind the desks just had way too much time on their hands to produce such a crock of fecal matter (technical terms)."