The 450SA (ARF distributed exclusively by horizon hobbies??) & 450S (kit) are supposed to be the identical. I have the 450S kit & examined the SA too. Apparently the SA still comes with a z bend tail pushrod & split yoke tail contol.. whilst the S has full ball linked tail control (much smoother & no binding as i found in the SA tail control!

But anyway "fluffhead" from what I have read sofar, you should only get any of the SE versions specifically because the rotor head feathering shaft has thrust bearings in addition to the standard axial BB's making the collective movment etc.. much less STICKY so the machine is is much more precise! The head also features stronger 4mm feathering shaft, compared to a 3mm one on all the others!

I still prefer aluminum frame over carbon for it's durability so I stuck with the S (lie: hobby store only had those in stock! lol) & will just buy the complete SE head available for about $170 after I prang the head on this one!
Laters