I have been purchasing CLIR, Clearsign Technology. They make low NOx burners for energy/chemical industrials, nominally turning an expensive post burn cleaning process to a pre burn process. I bought it long ago relying on adoption of strict emission standards on national and state level, but before there was a market ready product, price of thinking I was a genius. But I have been adding as price dropped, and currently.
Main difference is that there is more proof of concept as CLIR has been booking sales. Plus where they figured they mainly be in refinery burners, there's been sales in horizontal markets, like recent press releases in chemical and power generation burners, and in Texas, Missouri, and Oklahoma, versus chiefly in California. Additionally, they claim and verified, that their burners can achieve similar results with emerging use of hydrogen as fuel. With the current sales, they are still a bit from breakeven, but seem to be suggesting it will be close.
Anyway, just wanted to share and also welcome any pushback.