my experience with magnet links is that they are unpredictably slow: sometimes it works almost instantaneously, sometimes it takes literally forever to fetch the peers and the transfer never completes. busiest torrents will of course propagate better...

I was hoping I could transfer semi-public files (say some music with a friend) without putting them on the public trackers, but my tests with different clients were not conclusive, so those really only make sense for busy, wide-distribution torrents and not one-to-a-few transfers, for which things like magic-wormhole are a better alternative.