The first monitor calibration device I owned was the original Optical Spyder, I think I had a “good” one as it did a reasonable job though I did hear there was variability in build quality and accuracy.
For some years now I have advised people to buy Gretag Macbeth calibrators as the results and consistancy were much better. For clients who already owned a Spyder I was happy to see if it produced a reasonable calibration (Im very sensitive to how my test images should look on a monitor).
However I have recently visited a few clients were the calibration was way out even though the correct perameters were used and the profiling process went without a hitch. Im taking here about a white point that was no where near 6500K and incorrect display of shadow detail. Pantone sell a range of Spyders from cheap to expensive – presumably the cheap ones are not as good as their expensive ones?
If you use a Pantone Spyder and you are getting poor calibrated repro/proof mismatches have a look at replacing it with a Gretag Macbeth Eye-one display 2.
(I have no connection with colour confidence so try a search on Google to check prices)