Most people have far more use for a proper deadlift than the type of exercise you are talking about.
The safer way to do the lift you're talking about is by using a hyperextension roman chair. I've seen people do this exercise with a bar behind their neck and two plates (225lbs). You can also do a straight leg dead lift. I've never seen anyone do this with big weights though. I have seen people do it with 40lbs dumbbells while standing on an elevated platform (8-12 inches). This was more about flexibility than raw power.
I don't know what you are trying to accomplish with your workouts, but I normally would advise against isolation exercises for anything except vanity muscles (bicep, shoulder, calf, etc). I've found that the rowing machine and one arm kettle bell swings translate very well to making my back strong at stuff I care about (working on cars, moving heavy shit, yard work, etc). If you are a power lifter then that hyperextension exercise is worth while.
Concur with rowing machine
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