Great, these are my go to needles for almost project.
I have probably knitted with every material you can think of - plastic, aluminum, casein, bamboo, ebony, rosewood, other hardwoods, tempered glass, and, of course, steel. For the heavy, fluffy yarns I am mostly using these days, steel works best, as it doesn't "hang up" the yarns as woods can even when well polished. Hiya Hiya delivers steel points which to my hands feel every bit as good as Addi, and the coils don't break and don't fall out of the points as happens with many non-steel needles and interchangeable needles. They aren't as relaxed as Addi cables, but I can live with that (Including a trinket or a pattern with each packet is also a nice touch.)
I really like these needles ( I have many in various sizes). Sharp enough to make stitches easily but not so sharp they cause sore fingers. For me they have the perfect amount of "slickness", stitches slide easily but I don't have problems with stitches sliding off the needles.