Also have a Tello for a year now and amazed at the quality and stability for the price. I only used it a couple of times. Only downside is lack of gps. I'm busy with a program for and Arduino or Pi0 to go onboard the Tello so that I can send waypoints via wifi as well as control the Tello.
I'm from richards bay. I hardly fly without the repeater anymore. It's very humid here so just flying of the phone gives you anything from 10 to 30 meters. With the repeater I can venture out 60 to 80m without any significant loss and with video at 3mb s in the Highveld with thin air you should easily go further. I prefer to keep it in sight at it gets very small from about 50m. I also have a gamesir g3s which I use wired to the phone to eliminate the gremlins that comes with Bluetooth controllers.