Dillon can use any 7/8 dies. Their dies offer some efficiencies in the their press though like spring loaded decaps pins and some other features.
Pros of the 550:
Quick to change for another caliber
Simpler in use
Doesn't auto-index (Con: Can also be a con which may lead to a double-charge if not paying attention)
Cons of the 550:
Can not use a powder check due to only having 4 stations
Pros of the 750:
Has more stations allowing for a powder check
Auto-index (Cons: Can create a bigger problem if load is wrong and not caught in time)
Cons of the 750:
Slower to switch calibers if loading multiple calibers
Components more expensive (quick change systems, etc)
