I bought this at my local guitar store...not through Amazon. I've probably have purchased 12 of these for my guitars and 1 for my ukulele. Overall, considering all the options - this is still the best in case guitar humidifier. It tells you when to refill it when it shrivels up. Keeps the guitars humidified while in the case closed. It won't work with a gig bag or guitar on your stand...why - I had a GS mini in the gig bag and its too porous so if its in a dry area near a fire place, outside wall, or you live in a desert - it won't work well. All humidifiers depending on the condition may not last long. I still would buy this over others...the humidipaks sometimes have been known to leak in guitars. The planet waves sponges can mold up - both old and new ( I use distilled water in them). If you want this to work well - you need a nice Geib or TKL hardshell case with a seal, not a chip board case.

Why didn't I give it 5 stars - no instructions - once I found out I had to go online or go to the Unofficial Martin Guitar Forum or Acoustic Guitar Forum to learn how to properly prevent leakage. I've had 4 failures of older models. I think the glue was stiff and I left it dry in the summer so the crystals sticking together and causing damage to the membrane will cause failure. I through these out since its cheaper to buy a new one than damage your guitar. Its cheaper to spend 20.00 than repair cracks, polish and crown frets, cleat separations, etc. My smaller body guitars use less than the dreadnough size guitars.

Overall - it's better to have a sponge in your guitar than nothing, but its even better to use the Oasis plus - especially during the winter months in the North with the heat on. I did purchase at EVAP3 Vornado - to complement this humidifier. I bought the GS mini SKB case to rehumidify my travel guitar after I felt some sharp frets due to fretboard shrinkage...after adding this along with the case the GS mini is happy again.
I bought this at my local guitar store... not through Amazon. I've probably have purchased 12 of these for my guitars and 1 for my ukulele. Overall, considering all the options - this is still the best in case guitar humidifier. It tells you when to refill it when it shrivels up. Keeps the guitars humidified while in the case closed. It won't work with a gig bag or guitar on your stand... why - I had a GS mini in the gig bag and its too porous so if its in a dry area near a fire place, outside wall, or you live in a desert - it won't work well. All humidifiers depending on the condition may not last long. I still would buy this over others... the humidipaks sometimes have been known to leak in guitars. The planet waves sponges can mold up - both old and new ( I use distilled water in them). If you want this to work well - you need a nice Geib or TKL hardshell case with a seal, not a chip board case. Why didn't I give it 5 stars - no instructions - once I found out I had to go online or go to the Unofficial Martin Guitar Forum or Acoustic Guitar Forum to learn how to properly prevent leakage. I've had 4 failures of older models. I think the glue was stiff and I left it dry in the summer so the crystals sticking together and causing damage to the membrane will cause failure. I through these out since its cheaper to buy a new one than damage your guitar. Its cheaper to spend 20. 00 than repair cracks, polish and crown frets, cleat separations, etc. My smaller body guitars use less than the dreadnough size guitars. Overall - it's better to have a sponge in your guitar than nothing, but its even better to use the Oasis plus - especially during the winter months in the North with the heat on. I did purchase at EVAP3 Vornado - to complement this humidifier. I bought the GS mini SKB case to rehumidify my travel guitar after I felt some sharp frets due to fretboard shrinkage... after adding this along with the case the GS mini is happy again.