I use a combo of beads and gel/foam. I have a 500 count humdidor so I'm looking to keep the humidity as even as I possibly can throughout my entire humidor. I alternate between foam/gel and beads between drawers/levels.

I've personally noticed with beads that I have to re-hydrate them more often than the other humidification devices - but they do tend to keep the humidity a bit more even than foam or gel. I've also noticed that the beads do start to turn brown over time - I'm assuming that is the attributed to the oils in the cigars making it into the beads.

Even if you faithfully use distilled water to prevent bad things in tap water from leaching into the beads - beads do have a shelf life. You probably should replace them every year or three (depending on how they're doing), just as you would floral foam or gels.