After spending literally hours looking for the perfect heater for my Fluval Edge. I've bumped into this thread. Genius!
I know it's an old thread, but this has given time for the OP and other people to now have a definitive opinion on the mentioned Hong Kong compact heater, and the technique of mounting it within the HOB filter.
How are people getting on with this? Is it working out OK?
My tank has finally completed the nitrogen cycle and I'm dying to get stocking. But my heater isn't working now, so I need a replacement!