I've never flown one, but my understanding is that it requires an endorsement because it doesn't fall into the "Single Engine < 5700kg" group -regardless of their positioning, there are still two engines.
The centerline thrust thing comes up in regard to the need to have a multi-engine CIR or NVFR rating to fly one under the NVFR or IFR. Given the lack of asymmetric thrust issues, there is no reason you can't operate it under the IFR or NVFR on a single engine instrument rating. You do still need the type endorsement though.
Clear as mud?
