Bundling multiple files into a single .zip makes them easier to share, upload, or archive. This tool builds the zip archive locally in your browser using standard DEFLATE compression, so your files are never sent anywhere to be zipped.
Yes, photos, PDFs, videos, folders of documents, anything. The tool doesn't restrict file types.
Yes, it's a standard .zip archive, openable natively on Windows, Mac, Linux, and mobile without any special software.
It depends on the file types. Text-heavy files compress well, while already-compressed formats like JPG or MP4 won't shrink much further, since they're already compressed.