From my recollection, Visa and Mastercard both provide secondary CDW for 15 days max with a $50,000 limit and AMEX provides secondary CDW for 30 days, also up to $50,000.
AMEX's insurance (I think Visa's too), will not cover full size SUV's and pickup trucks (AMEX specifies Chevrolet/GMC Tahoe, Yukon and Suburban, and more) I think Mastercard will cover Suburbans etc. put not pickup trucks.
There are occasional Visa/Mastercards that have other insurance which have other terms, like OPP that has primary or Citi AAdvantage world MC (30 days).
With AMEX's premium insurance, the advantages are:
1) Primary coverage
2) $100,000 limit
3) Cover more car categories, including full size SUV and pickup trucks
4) Coverage up to 42 days