Hi,
The QL is not the same as the Quick Nautic.
The QL is the same as the Mobitherm. The Surcal I don't know. What I know is that the Isotemp is best from the test and also my experience is good. The Original QL 20L lasted only 5 years. After that the SS tank was fully corroded although it is 316 SS. For the test see attachment.
Regards,
Ger