I've been using
Revelate's Mag-Tank bolt on bag, and the bolt on connections with the top tube seem pretty secure, for anyone wondering. When shopping for a bolt on bag, I was surprised how few of them are out there. I guess the bag market hasn't quite caught up with how prevalent the top tube bosses are becoming.
Anyway, I like the bag overall. The magnetic clasp seems a bit finicky, but I haven't had much time with it, so hopefully I'll figure out methods of securing it so that it doesn't become unclasped during a ride.