It's really not a substitute for mobile safari at all, especially not mobile safari at a specific iOS version. The state of the art there afaik is still to have a drawer full of iOS devices you hold off on updating for a couple years, or else you can never reproduce the bug that your users on older iPhones see.

There are too many bugs with things like the collapsible url bar / jank when changing orientation / or just plain bugs unique to their cut that won't reproduce on arbitrary WebKit browsers. I've had to fix layering bugs 100% reproducible on mobile safari on device but not in the emulator or beta for the new iOS at the time.