The only significant difference (other than the cool looks and the extra weight) is that the blades are two inches shorter on the three-blade, resulting in a bit less blade erosion when operating on the ground, and quieter operation due to reduced tip velocity.
FWIW: This was a tough decision for me, but in the end I opted for the 3-Blade. The decision was based on what I heard about landing-light-life in the 2- vs. in the 3-blade configuration. I’m concerned about vibration levels, not the cost of the landing light; but it seems like a reasonable barometer. Less vibration means an easier life for gyros in particular, but also for connections, couplings, avionics, occupants, etc.
All the 2-blade owners I spoke to or emailed reported a need to change landing lights every 40-50 hours, almost regardless of how much they used it. On the other hand, most (but not all) 3-blade owners said that the landing light lasted much longer. Walt told me that he has yet to replace his - I believe he has over 400 hours so far.
Another factor is the frequency of the cabin noise. When I visited the factory, someone (don’t remember who) told me that the 3-blade installation results in a frequency which is closer to the design-point for the Lightspeed headsets, so the noise cancelling should be more effective. I don’t know whether other manufacturers design around the same frequency, but I use Lightspeeds.
In the end, though, there’s not much in it; especially considering the $$ and the extra weight. Be careful about the prop weight - the sample W&B schedules I requested showed a 23 lb difference over an otherwise identical 2-blade installation.
I’m still not sure I made the right choice, but at least I feel like I did my “due diligence”.