So it's an electric boiler, but with a solid core. I don't really see the benefit tbh. It's going to be wildly expensive to run as it's basically a fancy storage heater?

Its capacity is 40kWh.  That's not going to last very long in winter then you'll be on to peak rates.  It is what it is I suppose - a big storage heater. 

The trials with these sort of devices are using much lower tariff.. I have seen 12p an hour, and not just a fixed 4 or so hour period overnight. 

This will help test the viability of energy suppliers charging the device automatically at cheap times throughout the day.

This being an alternative to a battery/solar/ashp setup which part of the market is evolving to. 

I suspect it will always be quite niche but may work where there are space constraints etc, suitable tariff, relatively low heat demand etc. 

Be interesting to see how popular these sort of energy storage systems are in the future. 

Probably their target market is flats. My old flat was all electric and storage heaters, which were frankly useless and wasteful, and barely lasted a couple hours in the morning. This thing is a bigger, better storage heater that apparently actually stores heat, which I would have installed in a heartbeat at the time. The only question mark would be the weight of the unit - it would have been suitable for my flat, but probably not everywhere.

Robert Llewelyn off the Fully Charged show installed one of these if you haven't seen it on Youtube yet:

(interview with Tepo)

https://youtu.be/XZZisnQi7Ww  (tour of his house - ZEB install is at 10.23mins)