'a lot more refined' is putting it mildly
This is where we tend to disagree, I don't think the product itself is over priced. Sure you'll be able to buy the same capacity for half the price but the cells are only half the product and of course you could put together a DIY solution for a lot less.
The gateway alone is £800 and is optional, 6kw inverter isn't cheap, its for a liquid heating/cooling system, the systems are scalable, its outdoor rated, has excellent software, a long warranty, proven reliability and decent support. None of that stuff is free.
@danb21t - an alterative but similar option to the Tesla Powerwall is the GivEnergy All In One, its basically the same product but slightly cheaper. It lacks a liquid heating/cooling system but its a few hundred cheaper and has a slightly better ecosystem (charger, smart plugs etc).