While pistons are cheaper than turbines, that’s because almost all of the approved pistons on the market use 1940s or earlier technology. They are very, very, very simple machines. They are still extremely expensive.
This engine is very complicated, even for an automotive engine. It’s got some revolutionary attributes, but it also has a bunch of single points of failure that would mean traveling in this airplane over long distances and large bodies of water isn’t a good idea.
I’m frankly not holding my breath. While they’ve got a bunch of buzz around them, that and a working example are like 1/10 the battle in the aircraft industry. Wish them the best for trying to advance the art but many more established and better funded folks have tried and gone bankrupt before them.