Well, yes it can be operated with one hand, just a simple twist. There is no detent however so you need to use a little bit of your eyes. However it is stiff enough that it does not turn on it's own. For more details ask Luis.
The PMDSV alos is still my favorite, a simple plug because I also much prefer the curved mouthpiece.
I have made a number of dives with it, one in cold water and low viz, worked like a charm but I was careful to keep track of what I was doing. The "keeper" bands act as an alignment witness.
N
Nemrod
I have changed the two DSV clamp to line up with the mouthpiece and it makes it a lot more intuitive to line up the opening this way. You should change yours and try it this way. I think you will like it.
I left the two hose clamps in the normal forward facing position.
An extra advantage is that it looks more like the original un-modified mouthpiece.