For years I'd used those long wooly 'pad savers' in my saxes, before I realised that they were probably holding moister inside the sax. When I stopped using them I needed to get an end cap to make up the extra space in my case, and being adjustable the Gap Cap is great for that.
A side note, the one I got developed a problem so I dropped gap cap an email in the US. They were absolutely great and sorted it without question. They then went on to revise some elements of the product. Not only did they listen and understand, but they did something about it... that's worth paying for in my opinion!