No matter how I secure it, unless I roll the top of the gel packs into the part of the pouch that's supposed to fit into the plastic securing pieces, the pack sits on the inside back of the guitar and the plastic pieces are loose enough to move around and mar the finish on my guitar.

Granted, I exceeded the recomended usage by 25% and when I opened up the case they had leaked out of the mesh container, into my Martin and stained the finish clear through to the outside!

If you have a guitar costing many thousands, you do not want to risk marring its finish with a humidifier

hard plastic clip that holds cloth humidifier bag closed can scratch finishes

Granted, I exceeded the recomended usage by 25% and when I opened up the case they had leaked out of the mesh container, into my Martin and stained the finish clear through to the outside!

I don't think the contents are corrosive, but 100% humidity maintained on the surface of wood causes finish damage, warping, blistering and delamination, mold growth, and more

The new plastic retainer has sharp edges that could scratch the finish on a guitar