As a user, I hate Sparkle. At least, I hate Sparkle's default mode where you have to click "Install Update", then wait for the update to download, then authenticate, then wait for the update to extract, then wait for the app to relaunch. Too slow. When I open an app, I want to use it, immediately. I'd rather have apps update in the background; barring that, at least give me a button to manually start a background update while I continue to use the older version of the app.
Sparkle does have that for a long time now, but the default does still want you to agree to background updates the first time. Developers can turn that off and make apps update silently in the background (when they're running).