IIRC, Henry @ Alpha said the 4-wheel version definitely sticks much better on the track allowing higher cornering speeds.
Also, while I thought the nanny controls were lost in the conversion, I seem to have seen a post somewhere that at least one conversion preserved the safety systems.
As far as the conversion goes, I'd imagine it would be treated as a kit vehicle in most states or at least those states that have such a classification. Of course, if the state uses just the VIN to determine category, the vehicle should remain a motorcycle or autocycle, depending on the particular state.
I'd consider a 4-wheel conversion IF they could get the price down to below $8K (unlikely, due to lack of volume) AND if the safety controls can be retained.