what brand would you recommend? I don't want to buy from a bad brand, or get one that's unreliable.No. Analogue measurements are not accurate. Those devices are designed to stick to the wall of an enclosure. Your tortoise lives on the floor.
You're better off with a digital temperature gun type thermometer which does good spot checks. (You should be able to get one from
Amazon or a hardware store for under $10. )
For humidity get a separate probe type digital hygrometer. Again they're not that expensive. The probe can be placed in the actual location that you want to measure.