Wow! This would be fun to use!
I don't see how this would be any less efficient than new commercial gas dryers built today. Unless you are thinking about the standing pilot light Vs. electronic pilot light. Most commercial gas dryers of this size built today are about 90,000 BTU or larger and would have the same efficiency as this unit. Gas dryers have not been redesigned like Gas Furnaces that have become more efficient over the years. In fact gas dryers of this size manufactured today have this same burner set up, blower system. Perhaps the electric drive motor's are a little more efficient.