Repetition on deads can be dangerous because of form degradation. For this reason I think it is best to leave the weight DEAD on the floor, re-grip and do the next rep, instead of a continuos motion. They are DEADlifts after all, picking up DEAD weight from the floor every time.
It's the only exercise that can kill you.
That's why it called a deadlift.
I do them in a rack,
and don't go all the way. It doesn't make a lot of sense. The lower you go, the more you have to use your leg's and make it a leg excersise, while the main goal is the lower back.
Stifflegged, but not locked, is imho the best, but not all the way.
Sometimes I also do them on a box, and go beyond the box, but always with light weights (not ronnie coleman light weights)