Hello again
I might be able to give you a bit of info, (some of which might be rubbish), there are lots of expert knife makers and collectors on bcuk that will be able to give you something more precise.
From what i gather, hrc is a measure of a metals hardness on the "rockwell c" scale. I think there are a few variables in what gives a blade its hardness, including steel type and how that steel is heat treated and tempered. Basically, the higher the number , the harder the blade. Desirable hardness varies depending on what the blade will be used for but the basic balance for knives seems to be around ease of sharpening, edge retention and toughness without being prone to chipping or snapping. I think, basically, if its soft, a blade will be flexible, easy to sharpen but it wont hold an edge well and will need regular sharpening. If a blade is very hard it will hold an edge very well but it will be more difficult to sharpen and it will be more brittle (metal drill bits are very hard to cut steel but they snap and break easily.)
I don't know where hrc59 falls on this scale, i think its pretty hard but reasonable to sharpen. As its a fallkniven, i'd guess it will be excellent and will handle everything you can throw at it . The idun has a laminated "supersteel" blade which is designed to be extremely resiliant and hard, with excellent edge retention yet remain flexible enough not to be brittle.
Hope this helps in some way and my apologies if it's not accurate , i'm sure someone who knows what they're on about will clear it up or fill in the gaps