According to Aviation Consumer the engine would drive the propeller directly (no gearbox) and due to the reduced coupling pulse even metal propellers are possible. Also according AC (but it's an article from june 2009) the main problems would be high oil consumption and of course the failing of some of the more sensitive components now and then.
I really hope they get the job done and bring out a class A product. You can argue endlessly about the need for an aerodiesel engine, but if I see that petrol companies
nowadays don't have the slightest interest in distributing lead-free avgas when it already exists then I know I shouldn't expect anything from them. Too bad for Hjelmco and GAMI who do an excellent job...