I bought this footswitch to use it with my Boss Katana 100, and it does the job.
The first button switches between the first channel and the second channel. And the other button switches between your A & B library of channels. The Katana-100 has 4 channels on the A library and an additional 4 on the b library. I first thought that it'd it swicth between 1-4 on A, but that wasn't the case. I did not know about this before which is why i only gave it an overall 4.
The build quality is decent, you can see some wear on the buttons, but it doesn't matter that much. I've never used the footswitch with shoes if that changes anything, and I've been using it basically every day since I got it. It doesn't feel like it'll break anytime soon.
Strongly recommend!
Edit: Rewrote middle section 2019-03-31, since I acquired new info.