You sure that wasn't for Strongman?
Ha, that was my guess too...! Didn't Kevin Nee pretty much tie himself to the car deadlift once.
Anyway, on the cart with the guys who use them as another tool in the box okay, not exclusively as my lower reps, get the mixed grip work, but why not use em at times? Why limit yourself to training the hips, legs and back hard, if your grip is the weaky link. Grip work is much easier and can be done anytime really or at least about 4-5 times per week.
Hook gripping can work too but it is bull hard doing higher reps.
Another point I think is valuable with deadlifting higher reps is when you used a mixed grip, your body is torquing in a certain direction with one arm out and one arm in. If you use straps and are pullling a heavy 7th or 8th rep, that might be something to consider.
Bent rows, RDL's, SLDL's, surgs all get the straps mostly.
Lastly, I change my mixed grip on nearly each set also, pulling with rt hand pronated lft sup, then switch lft pronated...