Instant Take off is not workling whole time.. after a time it is same speed like usually
Instant Take off is slow like usually after a time
If you are using Mini Copter Options https://umod.org/plugins/mini-copter-options then make sure your lift is set the same as in Vehicle License's plugin, which in your case is 0.75, and by default I believe Mini Copter Options is set to 0.25
Either what TheBear said (or another plugin modifying it), or it could be the term instant take-off may be misleading, since its more so instant start up. When you enter the helicopter, it will instantly start up its engine rather than the typical waiting you'd have to do for the engine to start up before being able to take off and fly (hence why I originally chose instant take off)
I tested this and it's working as intended. Personally, I don't care for it. Seems to take off a bit "unstable" for me, when it is set up this way. Call me "Old School". But, at least it's a choice!