All my bikes as a kid and teenager had coaster brakes and I never had any complaints about 'em. Even on some steep downhills they were adequate. But kids tend to like the sensation of slamming on the rear brakes to skid to stops. Seemed like fun when I was a kid. So I'm not sure my nostalgia goggles are reliable.

I suspect the trick is matching the tires and anticipated road surface to the coaster brake characteristics.

My notion of a short hop errand bike would still be a 3-speed IGH with coaster brake, maybe a front brake for security (I don't bounce as well now at 58). If I had my druthers - and the budget to match - I'd like an SRAM 2-speed Automatix set up with rear coaster brake, an inexpensive front brake, on a very utilitarian looking frame with front and rear baskets. Something fully functional and reasonably comfortable for up to 10 miles, but as anonymous looking as possible in hopes of deterring thieves. I figure anyone who'd steal a 40 lb beast like that probably needs it worse than I do for basic transportation and errands.