I have the Leopold, too, and I really like it. It has a "swollen" ridge near the front of the handle that makes it easier to hold onto.
The plastic ring pullers often have "legs" that are pretty thick and it can be hard to force them down between the keys. Unfortunately, although the skinnier-legged ones are easier to use, they are also more fragile. I prefer the type in the OP to the circular rings.
For "conventional" caps I use a wire puller and grab opposite corners and pull straight up. For 2-piece buckling spring caps you sometimes get both pieces if you aren't careful, but that doesn't really matter. Hi-Tek "Space Invaders" need to be grabbed on the sides, never the corners, or you will pull up the top of the switch body and they are fussy to put back together, besides the fact that you can lose springs.