I got The String Cleaner as a a Christmas stocking stuffer. Since then, once a week use on two guitars hasn't left it with any noticible dirt on the microfiber cleaning pads although their color may not be as bright as when new. My daily guitar hygiene of clean hands and wiping down the strings with a cloth may explain why I haven't seen any accumulation on the pads. FYI, recommended use is "after every use of your guitar" which I don't do.

Note that the pads are cleanable; "Clean once every 2 months or anytime the instrument is restrung. Lightly hand wash with warm water and a drop of liquid soap. Gently pat dry with a cloth or paper towel and leave open to air dry..." I haven't done that either but it sure sounds like the device is going to last along time.

The only negative I can come up with is that the device won't slide all the way to the nut given the action on my guitars. But it does get right up to or on the first fret.