You can download the official first demo for TeamJumpers Remastered on gamejolt!
(Note - Make sure to turn off your antivirus before installing it, because, for some reason, antiviruses don't like to run the game).
Anyways, you can download it here -
https://gamejolt.com/games/tj-rejumped/567092
Also here is a trailer with a lot of coverage on both TeamJumpers 2, and Rejumped :)
Enjoy :)