HEIC saves space on iPhone but is still not readable everywhere - older Windows machines, print shops and some web tools reject it. See HEIC vs JPEG.
There are quality controls so you decide the trade-off rather than accepting a fixed setting. Converting without losing quality goes through it.
Yes, EXIF is preserved. Output formats include JPG, PNG, WEBP, HEIF and PDF, in true batches.
No - conversion is local on macOS, with drag and drop and a Finder context menu entry.
You’re browsing inside Instagram, and its built-in browser isn’t allowed to hand links over to the App Store. Open this page in Safari and the link will work.
Tap the three-dot menu at the top right, then choose Open in external browser.