@RvP10,
The Happiness Box
Since the scenario explicity warns of the historically permanent nature of the experience, anyone stepping into the box is committing slow, albeit pleasurable, suicide. As I'm not ready to totally disengage from real or virtual life, I think I would take a pass.
Of course, unless the mechanism fails, once you got hooked up there would never be a moment of regret.
The Experience Machine
Having the ability to disengage from the machine makes for too easy a choice.
My only concern about using this machine would be what effect there might be of not having either random or unpleasent experiences.
Since the machine removes your awareness that you are living a selected, virtual experience, I suppose that randomness will, to some extent, be simulated, but if there is value to true randomness it will still be lost.
Contrast is usually necessary for appreciation and so I would be concerned about what the impact of a lifelong succession of only pleasent experiences might be.
This could be resolved by programming for the occassional unpleasent experience. Once again, the machine's ability to remove awareness that it is being used should not diminish the effect of unpleasent experiences, but there would still be the issue of randomness.
Since length of usage can be controlled though, it will be an easy choice to test the machine for several years and try to determine if there are any ill effects from losing randomness.
Since the ill effects might only manifest over a lifetime, a satisfactory test period would provide no certainty and so at some point a choice will have to be made whether emmersion in permanent of not. The longer though that one lives within the machine the less of a independent life one develops and so ultimately there may be really no choice at all save dying in the machine's world or dying in reality.