What an interesting puzzle. As a relative newcomer to Listeners on a regular basis I find the ones that need a lot of cold-solving a bit off putting: I really find the checked letters hugely useful to helping me solve obscure clues, and boy were some of these obscure! And I was doubly wary of this one because even after cold-solving most clues I was thinking the grid insertion would be hard because the usual deductions wouldn’t apply since there were six totally unknown entries. But in the end I cold-solved all but about ten, then started toying with grid filling, found it went easier than I dared hope, then the first replacement i got a few checked letters for (NW corner) gave me the theme and scales fell from my eyes. Very nice. I still prefer ones that don’t rely so heavily on cold-solving, but am pleased to have managed to do one without much help!
PS what is “PDM”?