Some years back I was experimenting with doing seated pulldowns on a 45 degree angle, and I maxed out the weight on the stack. As an experiment, I tried this single arm version you see here. It worked better than the bilateral version did.
Because of the 45 degree angle of the weight and sitting on the floor, you can do these quite heavy, and they build the strength in the Lat to be able to do chin-ups and pull-ups.
I prefer the 6-10 or 8-12 range. Usually for 2-3 sets.
Notice these are done slow and controlled. The movement is self correcting and requires proper technique by default.
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