It depends on what you mean by 'safe'.
The higher you go, the more likely it is that the optical flow sensors will not be able to keep Tello stable and, particularly if it is windy, the Tello could drift away (changing to Fast mode can help correct this).
Also, the higher you are the more you risk your wifi connection becoming weak which brings a risk of loss of control and poor video feed.
If you wish to try/risk greater heights, then it is better to use a wifi repeater and a (very) calm day.
Hope this helps.
I am too frightened to go above 10m.
Is there a way to reset it back so it also doesn’t hit the floor after you change the setting?
Seen someone say changing the limit allows Tello to hit the deck haha