Unfortunately, no one can give you a general answer because the devices transmit in the 2.4Ghz band and it depends on how many other signals interfere and on the condition of your flat.
Wireless mice and keyboards, as well as WiFi, also operate in the 2.4Ghz band.
I, for example, have several such devices and a specially powerful Wifi access point in the same room and can be up to 8m away from the transceiver with only rare problems.