HDRs don't seem to be particularly well known here - you might get more insight from people on North American boards as they've been a popular saddle there for ten years or more.
There are 2 types of HDR over here, the "cheap" type that were distributed by Shires, and the not so cheap ones! The not so cheap ones are gorgeous, and not dissimilar to the "Big name" french saddles. The cheap ones are horrid, tight over the shoulder, and rubbish leather which wears badly Check what you are buying in the flesh if possible
I have a HDR Rivella. It's good points: very comfy seat, hard wearing, puts rider in good position. The bad points: does not fit a wide range of horses, the cantle tends to rise up & down when riding rising trot.