All the following are off the top of my head, so apologies if any numbers are a bit out.
In terms of the performance, etc, the AE300 is smoother than the Thielerts across the rev range and gives better climb performance, requires a lower percentage power setting for a given speed and (speed for speed) gives similar fuel burns.
TBO is currently 1,000 hours but is expected to move to 1,500+ before too much longer. Unlike the Thielert, the AE300 can be overhauled rather than requiring a complete new unit.
It's not a cheap upgrade at €99,000 plus VAT but compared to fitting two new Thielerts there is actually little difference in overall cost - so the savings are due come from much lower maintenance costs. The upgrade includes quite a bit of work on the undercarriage, beefing it up and giving a higher MTOW.
Overhauls are currently quoted at about €18,000 per engine which is a bit over half the price of a new Thielert.
Diamond Aircraft :: Austro Engine Upgrade
Off the top of my head, I believe that the gearbox, fuel pumps etc are all lifed for the life of the engine with just routine service items such as filters needing to be replaced.