I'm using the powderfunnel PTX in my Hornady LnL powder measure. Works like a champ, and the beauty of it is that you only have to buy one PTX; it'll work for all sorts of handgun calibers.
I wanted one because I wanted a powder checker in one of my LnL stations. I chose the RCBS Lockout Die because to me, the Hornady Powder Cop did little more than my looking in the case each time. And since the Powder Cop requires me to look each and every time, I wasn't happy with it as a failsafe.
The Lockout die will stop the completion of the stroke if there is a squib load (no powder drop) or a double load. In fact, it'll even catch partial loads, though RCBS won't advertise it as such.
I was reloading a couple nights ago using it, and it caught two mis-drops. The rotor stuck in the up position, and didn't drop down as the ram lowered, meaning no powder was dropped in the next case. (I added a little graphite to the sliding parts, problem solves). But the point is the Lockout die caught it for me; maybe I would have been looking at a Powder Cop, maybe not.
And FWIW: I use the FCD in my last station.