Well my living room is defiinitely smaller than 50 square metres and I would imagine most people's are! Granted I never shut the door completely, but I've had a feliway diffuser in there since last April. I think my room's a bit bigger than yours, Charlotte, but not a lot. I would also recommend getting the spray too as that's more concentrated and instant whereas the diffuser takes a while to kick in. I think it's very effective - I take a spray to the cattery when they go to help them settle in. I have the diffuser in the living room and give the rest of the flat an occasional spray. I have sprayed the living room when the diffuser has been in use. I wouldn't have thought you could overdose on it but tbh that had never occurred to me.