The OWL Monitor is simple to fit and offers several programmable options say to put in tariffs to estimate your bill etc. Admittedly though I use mine really to look at the instantaneous energy use and the temperature (also shown on the display).
I have it in the kitchen and so can see at a glance how many kWh are being used at a given time. I quickly became familiar with approximately how much should be showing at particular times during the day. When I look at it in the evening say, if it is reading high and I know nothing big (tumble dryer, oven) is on I can say with near certainty that the spotlights are on in the hall rather than the lamp fitted with the CFL so I immediately switch off the spots and turn on the lamp. Similarly since seeing just how much the kettle effects the draw of electricity I am far more likely to make tea after the first boil rather than leaving it and re-boiling the kettle a few minutes later. I am much more conscious of switching off lights in rooms we are not using during the evening and not using the washing machine for half loads. And I have started hanging out clothes where as before I would just throw them all in the dryer.
I recommend the meter. If you are interested in trying to reduce your electricity use it is a brilliant way to help you change your behaviour. There is great satisfaction in seeing the readings come down as you make the effort to turn things off !
My electricity bills have come down, but I also switched supplier so that helped obviously, however we are definitely using less electricity than when we first got the meter so I am happy that it will pay for itself - at the cheaper price, not the Tesco one ! I must take out some old bills and do a comparison on the kWh soon.
I'm sure there are other meters that do the same job, I'm just commenting on the one I have and obviously I'm pleased with it. No connection with anyone selling these things.
Hope that helps !
-R