I have indeed never seen a positive one. (I take them before some face-to-face gatherings, including going to my 94-year-old neighbour's, and before and after cons.) I haven't had symptoms that seem likely to be Covid, but asymptomatic transmission is a thing, so.
With the original NHS ones I was supposed to snap or twist the end off a capsule. I usually used scissors. Out of 14 attempts I had 3 failures, because I couldn't get enough liquid out of the capsule and into the extraction tube. Peeling the foil cap off the extraction tube is an easier dexterity challenge for me, and I haven't had any failures.
Re: There have been a parade of different manufacturers
With the original NHS ones I was supposed to snap or twist the end off a capsule. I usually used scissors. Out of 14 attempts I had 3 failures, because I couldn't get enough liquid out of the capsule and into the extraction tube. Peeling the foil cap off the extraction tube is an easier dexterity challenge for me, and I haven't had any failures.