It is a great thing to do regularly and not similar to other strength exercises at all imo...good for all upper body joints and spine. Keep head up to keep spine straight. I have heard that as a gauge of fitness a 40 year old that can do 2 minutes at dead hang is in very good condition...
I am 66.5 yoa, 6', 210# and am up to solid 45 second hangs. Goal is 1:30 x3, 5 times a week. I think that dead hangs for longer duration done regularly over time increases upper body strength across the board and the benefits to the spine/spinal erectors and other shoulder and back muscles takes time and consistency to realize although big issues may improve fairly quickly.
What the heck, just do it for 6 months and see what happens.....I promise it will not be a negative result. There are so many non glamorous exercises that are very beneficial and we hardly ever see anyone doing those...