The color filters of any colorimeter or spectrophotometer will fade over time. That isn't really limited to one brand or another or even one model or another. As far as I know, though, X-Rite's devices are all spectrophotometers:
Actually it does vary a lot by model. Stuff like i1D2 and older Spyders have unprotected gels and they decay a lot faster than the ones with glass and sealing. i1Display Pro for instance lasts a lot longer than the old i1D2.
x-rite makes lots of colorimeters, i1D2, i1D, i1Display Pro and such were all colorimeters. i1 Pro and i1 Pro II are spectros as is one of the colormunkis (there is a new colormunki, man their new naming is soooo confusing! i1 Display Pro and i1 Display and i1 Pro are 100% different and the latter is a spectro and the first two colorimeters! and I think colormunki is a spectro but the new colormunki display i think is a slowed down i1 display pro colorimeters, i forget the naming for the colormunkis so that might be wrong).
i1 Display Pro seems to have the least copy to copy variation of all the colorimeters that do not cost like $800+. Spyder4 seems to be OK but not up to the i1 Display Pro.
Seeing as I plan to buy that NEC monitor, and I don't generally create printer calibrations anymore, and the $500 ColorMunki Design was just a bit expensive for me at the time. If you aren't intending to spend $1200 on a new monitor, though, the ColorMunki is pretty much the most accurate calibration device around. If you don't want to spend $500, then an i1Display Pro is probably sufficient (however, to be quite honest, I am not sure if that is a spectro or a colorimeter...either way, the reviews indicate it does an exquisite job.)
i1 Display Pro is a colorimeter but it has expanded vision compared to the prior i1D2 and it is VASTLY better in terms of copy to copy variation. I tested a few i1 Display Pro and they were identical for most measurements off by like 0.001 for a few and like .002 for one. The i1D2 were said to at times register, copy to copy, a color calibrated by one copy to measure 10 to even 20dE off often enough (not with all copies, but it wasn't that rare that their could be that much of a difference copy to copy)
i1 Display Pro having almost idenitcal performance for all copies means that the included conversion tables all apply well it has tables for regular CCFL, wide gamut CCFL, LED and such. it works especially well with NEC CCFL wide gamut PA monitors since that is the monitors they used to calibrate the tables.
It is much faster and somewhat more accurate at measuring dark shades than the affordable spectros.