Yes possibly of not much scientific value unless you can get a large enough number of observers in a given location and over a reasonable length time to beat down the variability (The key to success in citizen science projects) but I suspect this project by CPRE is more about public awareness of the issue and to get a conversation going than the actual quality of the measurement. Hence the use of an instantly recognisable constellation. Interestingly I met a casual observer from a nearby village the other day who had been lent a sky quality meter to monitor their skies by the Friends of the Lake District.
Robin