It doesn't matter if it's hardwood or softwood. Watch for the accelerants and odors that pine based ones can have. I buy mine for kitchen litter 40 lbs for $6. It's douglas fir, softwood, and there's nothing wrong with it. It's all the hardware store carries and it works great.
Pellets for horse stalls are also OK, as is wood pelleted kitty litter the unscented kind. Just make sure anything made out of pine is kiln dried otherwise you will have to air it out for several weeks before it will be safe to use.
I'd say it is probably the hardest of all bedding on their feet. A lot of people use it just in a kitchen area with fleece in the rest of the cage. Some people do use it in the whole cage and they will also mix a different softer bedding into it. Softer beddings like shavings or care fresh. Some people put a layer of fleece over it.
Personally I can't see how it is. It would be like us walking on a dirt/pebbled road barefoot. I use it in the kitchen area only because it is so cheap and very effective with absorption and odor control, and the rest of the cage is fleece flippers.