I'm new to watercooling, and have been doing lots of reading and one thing I noticed was after about 2 years ago people prettymuch stop talking about how great heater cores are. Is the fad just over now? Do today's rads actually outperform them? Is it just due to the fact that only DD seems to still sell a premodded one? I haven't been able to find any performance charts to compare them to today's commercial offerings either.
I guess if your on a tight budget and want a small radiator for $20 then you could try one out but it looks more like something you would put in a Steampunk build. Seems like they only have one size though.
Heater cores aren't used that often but perform relatively well because they are very similar in design to watercooling radiators. There are additional considerations when choosing a heater core over a normal watercooling radiator:
1. You have to fit some kind of fitting as the existing fittings might not allow tubing connection
2. You have to consider how to mount fans and then mount the heater core in or on the case
3. Some heater cores are aluminum, so you'd want to avoid them
4. Heater cores come in many sizes based on automotive needs, but in reference to the DD core you're discussing you still need to determine total loop TDP.
5. Heater cores are designed to dissipate much higher heat loads (automotive coolant at operating temps around 160-180F) so the wall thickness of the tubes and overall structure are much thicker. This means your lower water temps of a watercooling loop aren't less effective when dissipating in comparison to the very thin walls of a watercooling rad.