On iPhone, you download through Safari and the file lands in the Files app first. Follow the steps below — including how to move it into Photos.
No. The whole process uses Safari and the iPhone's built-in Files app.
In the Files app → Downloads folder. From there you can play it, share it, or save it into Photos.
Yes — this tool takes the video from its source on Snack Video, just like on Android and PC, so the result is clean. See the No Watermark page for the explanation.