Well run. Easy to use app. Excellent customer services.
I was with Tello for a couple of years, but left for a better deal elsewhere otherwise I would have given them five stars! Sad to leave as Tello were incredibly efficient, always answered the telephone/webchat immediately and did what they promised. This hasn't been the case with my new mobile company.
Bundles last a month and have to be purchased every month via the app or online. You can vary your bundle month by month to suit your requirements. Unused mins/texts/internet can be rolled over if you purchase just before the month runs out. Tello run on Three network, who have really upped their game in recent years. Never had a problem with getting a signal.