Honestly, when I developed the Histo Fix stuff I thought it was a nice idea, but I changed my mind in the meantime.
Of course the plugin makes the histogram look "better", but the image looks just like it looked before. There are other operations like resizing, sharpening or noise reduction that fix a histogram, too, as a side effect.
So I would say: It doesn't matter if the histogram looks messed up as long as the image looks fine.
There is only one case where I can imagine that the Histo Fix plugin helps a bit. If an image is already quite degraded and you still need to perform extensive correction on it, the Histo Fix plugin may help to keep the image from degrading further.
If you start from a photo with a "normal" histogram, small gaps can occure in the image after doing some correction. That doesn't really matter, because the image usually looks better after the corrections even if the histogram looks worse.
Generally, I'd say use a low as possible value in the Histo Fix plugin. The Histo Fix essentially dithers the image, so a higher bit value produces a stronger dithering.