Someone else on YouTube seems to have discovered Tendera motors. And here he's using them in what appears to be a Tendera powered hydroplane. (judging by how long the motor run is.)
He doesn't mention Tendera, unfortunately but perhaps I can persuade him to give them and us a plug.
Rocket powered Hydroplane
Actually this young man has mainy wild and wakky projects and his channel is worth a look.
In fact in this one he's making paper aeroplanes, including at the end a large R/C one and he says he has 15seconds of thrust.
So, unless someone is up to the same tricks has Tendera I'd say this one has a Tendera L4 in it.
Tendera paper planes