Can guests download the photos on their phones, or is this a desktop-only thing?

Phones are the primary experience, honestly. The gallery is fully mobile-friendly — guests view and download their full-resolution photos on any device, and the whole flow was designed around a phone in one hand at a wedding afterparty. People expect to save photos straight to their camera roll these days, and that works. There's no app to install, which removes the single biggest barrier to older relatives actually getting their photos.