>The article doesn't mention the costs or complexity in building each unit but definitely implies it's cheaper than storing it batteries, which makes sense if it's essentially a heating element buried in sand.

Batteries are more expensive than nuclear power so yes, anything else is better.

The issue is that we can't both electrify everything and use legacy heating applications. Going back the the 20th century idea of central heating/cooling is great until you realize the costs involved with adding all the plumbing to buildings which were never designed with it in mind.