I always lower the leg part and just do a pull up. What is the function of the leg part/weight part?To reduce your own body weight on a pull up. It's an assist to build you up to your own body weight basically.
Luckily, we haven't a machine like that. Just a setup that allows multiple grips (my elbows like the choice of a neutral grip) and anyone that wants an assist just uses an elastic band. I wouldn't think pulling up from a straight elbow hang as shown in the link is a good idea for one's elbows.
Hmmm don't know about the machine in the link, but the one at my gym has multiple grips at different levels as well. It's also an assisted dip machine. I definitely don't ever extend my arms fully on any exercise, just to the point of full extension as I don't want to over extend and work the joint itself.
I like it, I'm 220lbs (give or take) and I don't have the strength yet to pull or dip my full body weight, so taking 50-60lbs off is better than struggling from a dead hang. I envy shorter people often, it would be nicer to have a better size to strength ratio.