The Seagate FireCuda has a better TBW and MTBF ratings, which means it is rated to last longer. Significantly longer, with the 970 EVO having about a 1,500,000 MTBF and the FireCuda having a 1,800,000 MTBF, as well as a 3600 TBW (Terrabytes written) rating compared to only a 600 TBW on the 970 EVO.
The Firecuda 520 is an enterprise class drive as well, and has a much faster random AND sequential read and write speeds than the 970 EVO. Hands down the better option. However, if the price of the two Samsung drives is less AND if you can get the same usage from two M.2 NVME drives rather than one, and have enough M.2 slots for them, then either option is satisfactory.
I'd opt for the Seagate myself.