There have been reports of the fiber optic portion of the sight slipping out. This is probably the source of the 90 day stuff. Just glue them back in and you're set to go.
However, that does raise some concerns. I have them on one of my Glock 19s. Pretty neat. I've got 2 more Glocks that need nightsights, but I think I'll go with either Trijicon or Meprolight. I have Meps on my other G19 as well as a majority of my other Glocks. Not quite as nice as the fiber optics, but I pick either of them up better than the factory plastic sights.
I'm also told that the hieght of these sights may be an issue. From what I've read, they clear the plastic (Kydex) holsters ok. Most of these have a sight rib molded into the holster. With leather, I've read about these sights gouging the inside of the holster and nice brownish slivers or specs obstructing the sights. I wouldn't expect this from the mass produced leather, but holsters made by custom makers may very well be boned too tight for these sights. Haven't tried my G19 with TFOs in my favorite IWB leather yet (Don Hume H715M clip-on if anybody is interested). Did try it in my Sidearmor IWB and no worries.