Yes, umberto. As you see, Vimeo can make it harder. You can configure a video to not show any "download
" button, which does two things: 1) It makes it harder for anyone to download your video, and 2) You can please administrators who do not want to allow students to download videos.
But the bottom line is that a smart student who wants to watch your video offline, they can use screen recording software or even their smartphone to copy the video. (Sometimes students can be smarter than administrators! 😀)
Yes, you are correct. There is a cost to Vimeo. But perhaps you can have the person who doesn't want to allow download pay for the Vimeo subscription? Well, another trade-off decision to be made. 🙁