Is a walkie-talkie a radio transmitting device ?

I think it definitely counts. A walkie-talkie is a radio communication device. But why can't it be brought?

Each country has regulations on the power of the civilian channel band, and even registration is required. If you are not familiar with the regulations on radio equipment in the UK, and you bring it in rashly, it will be considered illegal if you are caught. If you are not caught, but you use it to interfere with the channels or bands used by the police or military during use, why cause trouble?

May I ask you, do you need to print the delivery order as a paper document, or it is enough to show the mobile version to the car rental company at the scene?

Best to print out.