I bought a couple of the Jaeger heaters for my 500L tank, but can't comment on how effective they are as I didn't end up using them as they are too long to be positioned vertically and be completely submerged in that tank.
A heater I am using in 3 tanks that I would thoroughly recommend is the Aquael Neo. Great design and seemingly very efficient. They use an LED system to indicate the temp the tank is at and whether that is under or over what you have set the heater at and, unlike other heaters I've tried, the temperature they indicate matches very closely to the reading given by my infra-red and in-tank digital thermometers. These replaced several Fluval E series heaters, which I found to be very poor - even ones that were overrated for the tank volume seemed to have trouble reaching and maintaining the set temperature.
