Absolutely true there are other devices (Osaka Gas releases one...

Absolutely true there are other devices (Osaka Gas releases one to the Japanese market this month) but ones like Stirling engines have to convert heat energy to mechanical energy and drive a genertor to produce electricity. Whenever this happens efficiency drops quickly. The German demand of 85% total efficiency is pretty high and I think will rule out a lot of the competition, and no-one else that I'm aware of has achieved 60% electrical efficiency yet. (Let's hope it stays that way.)
If Germany really do want to achieve that target of 25% it will require a huge number of units. They won't all be Bluegens but to pick up 5-10% of that market would be huge. And if they work in Germany it will follow on to other markets.

Cheers
GLB