The verdict
Upscayl is the open-source desktop upscaler people actually use in production, not just download once and forget about. Local GPU processing means no upload friction, no privacy concerns, no per-image credits, and on adequate hardware, real-time turnaround. For users handling sensitive material (medical images, legal documents, personal archives), the local-only processing isn't a nice-to-have, it's a requirement. The honest friction: setup is more involved than "open a web tool" — you need a capable GPU, you'll fiddle with model selection, and the interface is functional rather than polished. For privacy-sensitive workflows, bulk processing where API costs add up, and technically comfortable users, Upscayl fits. For casual one-off upscaling or users who'd rather not install software, a web-based alternative (Waifu2x, ImgUpscaler) is the easier entry point. Open source means the codebase is audit-able for compliance.