MEGA introduces feature that allows you to export files from Google Drive

Seems like just have to trust them that it gets encrypted without them keeping a copy of the key, but to be fair that’s not much different than when you import your Gmail emails into Protonmail. For some users it might be worth not having the hassle of re-uploading everything, e.g. if you have lots of large but non-sensitive files like a big movie or music collection.