I've used those before, but when I lose them which happens more often than I would like to admit especially when I was doing field service, I upgraded to using fine emery cloth 220 to 320 grit cloth will give a good polish on your contacts and remove oxides.
What I do is buy a sheet of fine crocus cloth (crocus cloth is made from iron oxide metal particles with a cloth backing).
I fold it in half to mark it, then I take some rubber cement and apply it to the non-abrasive back sides, then I fold them so the backs stick together, and I place a few heavy books on them, and let it dry overnight.
Then I cut them into approximately 3/16 inch strips by three inches long. I have filled a 3 inch by 2 inch plastic storage box full of them - a lifetime supply.
But the fiberglass pen works much better but you have to be able to have an unobstructed access to the contact - so I just take apart the key.
I find the fine crocus cloth works better than the burnishing tool.
73
DR