julian, a quote from the link above
"I haven't done detailed range tests with the Digitalk radios yet, but a one kilometre test, through various buildings and trees, worked fine without repeater assistance. Clear as a bell, no problem. Putting a solid hill in the way, though, dropped the range to only about 500 metres.
These little transceivers are specified as having an "up to five kilometre" range, and there's a good chance they'll actually manage that, in the absence of obstacles. In urban areas, a couple of kilometres is likely to be the outer limit, and any solid geographical features in between will massively reduce it.
In the absence of extreme terrain, five watt UHF CB transmitters can manage ranges up to 20 kilometres. If you're using a low power handheld, you'll be able to hear more powerful transmitters at quite long distances, just as I can hear the SYD01 repeater. But you won't be able to reply unless you get closer"