Thanks for the input.
The guy that owns these is a good friend of mine and a Finescale featured modeler. They have been very well cared for and very used also. They are not very old, two years at the very most for each. I'm considering picking them up to add to the AB arsenal but to be honest, I'm not sure I'd ever use them. At the moment (well, when I model. Havent touched the bench in five months) my main tool is the CR. The HP-CS backs up the CR with a finer line ability. I have a BR for those larger projects.
Admittedly, the HP-CS and the BR rarely ever see the air hose so I'm not to sure I have a use for the 4k and 5k.