I received some of these as a present. Basically they're a pen with a brush type tip and acrylic paint as the 'ink'.
I've tried them out - touching up the tail markings on some 1/144 scale WW1 aircraft - and they appear to be really useful.
I use metallic sharpies -gold, silver and bronze - quite a lot, I find them really useful, so I expect to find similar uses for these.
Here's the link to the page.
https://ak-interactive.com/product-cate ... c-markers/