I've never used one.
But Marantz have made some very well-regarded higher end portable recorders and I'd expect the PDM620 to be a good piece of kit.
The controls look nice and ergonomic, and I'm sure the sound is as good as any portable recorder of that sort, and they are all pretty good.

Compare with offerings from Olympus, Sony and others in the same price range. Solid State sound seems a good site for examining the competition.