What happens in summer?
To be eligible for the eRadiator, your home has to have... "an external wall" ... and the external wall is needed for venting (if you "turn off" the eRadiator, the servers don't actually turn off; the heat is just pushed outside).
Admittedly, without active refrigeration this is unlikely to work too well when the temperature outside is over 35 C.
EDIT: they don't mention separate electric supplies, so presumably the unit has a way of tracking its power usage and reimbursing the homeowner. Otherwise this is just a scam, because far more efficient electrical [EDIT: thanks 'votingprawn!] heat pumps are available for less initial cost. However, the non-scam scenario seems only to make sense as a business in cold locations.
How are you defining efficiency here?
Efficiency is usually defined as (useful power out)/(power in), and basically all the power that goes into a computer comes out again as heat, which in this case is considered useful. Not really convinced you could buy a heater that was measurably more efficient.
ETA: heat pump would do it, didn't spring to mind when I read heater though!
I'd change that to read "in cold or temperate locations."
There are plenty of locations in Europe for example that rarely have days over 30 C yet don't often get below freezing in the winter. Doesn't make sense to describe these places as particularly "cold."
if you "turn off" the eRadiator, the servers don't actually turn off; the heat is just pushed outside
This could be a supplement for existing systems, perhaps even a backup or to serve some use spikes. But definitely not a replacement.
There are only few days a year when it gets over 30 in Scandinavia & Baltics.