thats about it. most are constantly on and there fore only low wattage cables of that type should be used.
you can get thermostats which control both the cable and tank heater but they are quite expensive so I chose a low wattage one which seems to work quite nicely, when I touch the gravel it is slightly warmer than the tank water.
bioplast make a "thermal float" system which is basically a length of co2 hose coiled around the heater and then spread across the bottom of the tank in the same way you would a heater cable,
I have one of these on my main tank and they are high maintenance but seem to give me good results but I will probably replace this with either a dupla or dennerle one when I eventually strip down and clean the main tank.