Thanks for that link. They certainly have interesting products, and I never ran across them before. I like that they're on Amazon - so buying and getting is very easy.

I note the ones you mention are only 1/4" high, so the standard screws in the foot of a vibroplex will be too long to tighten. Easily fixed by cutting the screw or buying shorter ones. But i need of fixing before it can be used.

I use feet from McMaster-Carr, which are slightly harder (70 vs. 65) but taller, and easier to fit. Here's what I posted on the Bug group in 2020:

-xx-

"I've been meaning to post this for a while! McMaster-Carr also has a somewhat larger-diameter straight-sided model like those found on MAC keys. I use them on all my bugs, vibroplexes as well - the larger diameter gives more stiction. 

https://www.mcmaster.com/#9540K55 with an internal washer  

https://www.mcmaster.com/#9540K21 without an internal washer 

I preferred the ones w/o the washer - they seem to offer a bit better stiction on my desktop."

-xx-

Note that on a Vibroplex, the right front bumper will extend a tiny fraction - .5mm or so - beyond the frame. I ignore it.

Even with these taller bumpers, on one of the 10 or so bugs I put these on, the screw bottomed out before the foot got tight. Easily fixed with a washer because there was clearance for the head to be higher without extending beyond the base of the foot. 

73 Chris NW6V