I've been shooting 48 mp HEIF for the last year using Halide. Glad that Apple brought the feature to the native camera app; one less reason to use a 3rd party app.
The quality is good. Better detail than 12 mp and I prefer it to ProRAW in situations with good lighting. The only time I shoot ProRAW now is for long exposures at night. Shooting a picture at 48 mp, then downsizing it to 12 mp looks better at a pixel level than shooting at 12 mp natively. This shouldn't be the case, but it is. Try it out and compare at 100% and you'll see the difference.
99% of my pictures are still shot in regular 12 mp HEIF. My primary reason for taking pictures is to have a visual scrapbook of vacations & interesting daily occurrences, so for most of my usual purposes, I don't need the extra pixels. I'll only go up to 48 mp when I'm photographing something I plan to print and hang on the wall.
