I’ve had a zero radius sink for over 13 years. No toothbrush necessary to keep the corners clean. I clean the sink after dinner most nights using a soapy blue scrub sponge. No gunk build up.

I've sold and installed hundreds of zero radius sinks. I'm certain that if gunk in the corners were an issue, I would have heard of it by now.

I’ve had and have both. Zero radius is marginally harder to clean but with normal maintenance is fine. In my kitchen my main sink is a zero radius ledge sink, the adjacent bar sink is 3/4” radius.