[SLDLs and other "dangerous" exercises are another case in point. Having torn a meniscus going heavy on SLDLs, I recommend staying at 30 reps on those. Which BTW aren't really a back exercise, they are hamstring specific. I suppose it might be possible for one's back to be so weak one couldn't work the hams, but that's probably rare. A much neglected exercise, IMO.[/QUOTE]


Every exercise can be "dangerous" when done wrong.

Doing high reps/low weight is nothing like Hiit work(most Hiit work becomes aerobic pretty quick) you are doing more aerobic work then anaerobic with the workout you describe.
Also to start a "newbie" on something like that makes even less sense! You want them to build connective tissue, neuro- pathways and prepare them for bigger resistances your way will not and will probably lead to injury in the log run.
Using a sled/leg press takes away have of the exercise much less bang for your buck.
SLDL's are great but you gotta have some resisatance.