...it's about as efficient as a redstone engine...
I feel like I might be missing something, as the Buildcraft Wiki says that a Redstone engine produces 0.05 MJ/t, and this clockwork engine produces at a minimum 0.5 MJ/t, which is 10 times as much as a redstone engine and at maximum winding, 1.5 MJ/t, or 30 times as much as a redstone engine... In the respect of power produced it seems like this is not at all similar to a redstone engine, but instead to a stirling engine.