Any two channel transmitter and receiver is fine for the standard M3R-16. If you plan to upgrade to a front brake then it’s worth investing in a 3 channel transmitter and one that offers a brake mixing function.
There’s a wide range on the market from budget priced entry models through to top of the range competition radios. Modern day radios tend to last well, so it’s good to invest as much as you can afford.
The radios on the links from Kamtec should be fine for anyone starting out and both are three channel with a mixing facility.
Schumacher sticks radio- CR151 CODE 2.4G FHSS 2 Stick 3Ch Tx+Rx – click above for more details
Etronix wheel radio – Etronix Pulse EX3GPRO 3ch 2.4g FHSS Wheel Radio System – click above for more details