I haven't seen a feature comparison recently (I remember a panel discussion about this some years ago, but don't recall much substance), but I just wanted to point out that GlobaLeaks is a similar age to SecureDrop and may well be pretty mature. My impression is that SecureDrop is developed mainly by Americans and GlobaLeaks mainly by Europeans, and each might also have been deployed primarily on the continent where it was developed. If my impression is right, there might be an ongoing reason that particular groups of people are more familiar with one than the other.