Exedy Clutch kits

I see three different Exedy clutch kits offered as OEM

Part number 10803A Most expensive

Part number MZK1002

and also MZK 1007 on several listings on ebay all three are listed interchangably

The only difference I can tell is the 10803 is heavy duty and includes the Pilot bearing seal ??

I see other brands of clutches are a lesser price . ATZ foir one

Whats the difference in a stage one and stage two clutch ?

What would you buy ? Has anyone installed any of these , What do you think ?