Low flow shower heads can be more trouble than they're worth in older blocks, where they're incompatible with gravity-feed hotwater systems and place additional back pressure on older pipework.
Human dynamics is such that you'll perceive that the water is cooler simply because it's aerated, and will therefore increase the feed of hot water and consequently your costs.
If you really want to save the 10 litres per minute that a low flow showerhead will achieve, keep your normal showerhead, have a better shower for half the time, and enjoy it !!