I haven't used one. But for what its worth, this is what I think.
Any system such as this has its pros and cons. Whether it's good, bad, or indifferent really depends on what you are using it for, and very importantly, the negatives you put through it.
For example, if you have an available light portrait in which the brightest highlight is actually the face, then the automatic calculation of contrast will be wrong. It is like an averaging meter in that it has to make assumptions because it doesn't know what tone any part of the image should be. It bases its assumptions on the subject actually having a true black and a true white which you meter with the probe. Read the downloadable manual which confirms this. The manual also has a section, "Adjustments in Special Cases", which tells you when its automatic calculations won't work (caveats).
Then realise that its predefined calculations are based on specific fresh paper and developer combinations at a specific temperature. Your set up is bound to vary from this so you will have to calibrate your own working methods which is not a problem but is not an out of the box solution.
Then consider that if you know what you are doing and have calibrated your neg develpment and know how to get accurate exposure, then all prints from a similar lighting situation will have similar print time and contrast. i.e. they will print similarly unless you are doing fine adjustments. There is no benefit in an averaging meter for fine control.
So personally I see no advantage in having a system like this except in the circumstance where you have a range of negatives under varying lighting conditions with dubious film exposure. In that case, the savings in time and paper would be much greater. So for example, if you were printing for many other people, then it would be a useful tool to get proof quality prints first or second time excepting the special cases which are many.
Again, for yourself with well calibrated procedures, the benefits are much less.
If you print regularly, then you will be able to judge correct exposure and contrast for an OK work print first time anyway. If you print only occasionally, then an automated system may save you some time and paper. But if you print only occasionally it will be a long time before it pays for itself in paper savings.
These automated systems give technically correct prints based on high and low values. That is very different from an aesthetically correct print which includes burning and dodging and placing tones where you want them. i.e. most times it won't give a perfect finished print first time.
Again, assuming your own exposure and dev of film is good, then once you have a good quality work print, which can be achieved first or second time, the savings achieved in taking that to a perfect finished print will be none assuming you know what you are doing.
