Does Gumlet allow a certain person to download the video once?

Yes, using the Signed URL feature, you can restrict a person to download the specific video only once.
Just go with the following steps:

• Tap the Video dropdown menu and select Collections.

• Hit the pencil icon to edit the collection you have made.

• On the next page, click the Video Protection tab, and enable Signed URL.

There is a minimum limit, but you cannot set a 30-second expiry for a one-minute video. Otherwise, the video would stop playing.