It's a JPEG + gain map format where the gain map is stored in the metadata. Same thing, as far as I can tell, that Halide is now using. It's what the industry is moving towards; it means that images display well on both SDR and HDR displays. I don't know what JPEG-XT is, aside from what I just skimmed on the Wikipedia page.
Not having before-and-after comparisons is mostly down to my being concerned about whether that would pass App Review; the guidelines indicate that the App Store images are supposed to be screenshots of the app, and I'm already pushing that rule with the example images for filters. I'm not sure a hubristic "here's how much better my photos are than Apple's" image would go over well. Maybe in my next update? I should at least have some comparisons on my website, but I've been bad at keeping that updated.
There's no Live Photo support, though I've been thinking about it. The reason is that my current iPhone 14 Pro Max does not support Live Photos while shooting in 48-megapixel mode; the capture process takes too long. I'd have to come up with a compromise such as only having video up to the moment of capture. That doesn't prevent me from implementing it for other iPhones/cameras/resolutions, but I don't like having features unevenly available.