Yes, they are dangerous as you see they can kill you in a heartbeat if you let them. I couldn't look at all the pictures, I just don't stomach that stuff very well.
As for safety, it was pounded into me by a very cautious father who I thank God everyday for.
Never work on a PTO implement with the shaft still connected to the PTO. May sound overly wary, but I haven't gotten caught in a disconnected PTO shaft yet.
Don't trust your hydraulics too much-they can fail and be on top of you before you know it. The number of times I've seen someone up under a loader or an implement that is being held up only by the hydraulics I can't count and it scares me everytime I see it.
Never get directly between your running equipment (or your car/truck for that matter) and anything else in close quarters. I now a fella who's old MF with poor brakes pinned him to the chisel he was hooking up-he got lucky and survived.
Heck when I go to clean the underneath of my push mower I always disconnected the spark plug wire just in case. Oh well, enough preaching for now and just don't get in too big of a hurry.