Edit edit: it turns out I just misinterpreted the menu options.

I think you're right. I think I misinterpreted the menu due to some wording adjustments in the options. Their main page has "Silicone Rubber Rings" on the far left of the top menu, and then Rubber Ring Kit elsewhere. I that they just didn't want to write "silicone" all over the place, and I interpreted that as a choice between two products.

Edit: Added the kit in question to a cart, and it was in fact all silicone rings. Which is convenient and now I feel a bit stupid for not trying that sooner.

You're missing what he was saying. He didn't say buy a bunch and guess at sizes (although its so cheap that wouldn't really hurt much). He was saying some machines the factory recommendation is tighter than necessary, so go up **one** size. That's not guessing. You know what size the factory recommends and then know what size is one increment larger. That's just saying "I disagree with the factory on this post and will be fixing the problem myself" by going size+1.