patrick,
Welcome to the board ! Manual stretching can be effective in the intial stages of PE as a sort of preparation phase for the efforts to follow. The issue with manually created force is that the amount of effort is an unknown.Using the bib hanger or related product where weights are being used to create a known force you can better gauge the resistance.This becomes more important over time and will provide a get indication of your progress.
The other intangible is that with hanging you free up both hands so other tasks such as a little computer work can be done at the same time as PE. If you want to give manual stretching a try make sure and hit all angles; straight out, up,down, and to each side and do a sets of 3 with a 10 second pull in each direction. Make sure and do a proper warm up and hot wrap prior to starting and take it slow for the first couple of weeks. A couple of guys I know say they have made good gains in time with manual force.
If you have any more questions or this is unclear please ask.