The expensive one where you lay on you back and operate a bicycle pump like thing works well for me. It's very easy to control the traction because the increase in traction is both slow and calibrated. There is a guide to make sure you are pulling in the correct direction.

It does seems to help bring my scalenes and other neck muscles out of bad spasm if done in a slow manner with only light traction.

I think the brand I have is sanders. Medicare paid for it

The cheap device that use a water bag over a door to provide traction are to be avoided according to the PT (Peter Edgelow) that I went to. It's very hard to control the direction of traction in a way that is constructive and does not flare.