It's one physical drive: lower power consumption, smaller size. (Easier target for thin tablets and laptops, especially in terms of potential battery life impact).
Fewer parts, lower complexity: Less likely to have a logical failure (like if the RAID array somehow became corrupted, or the RAID controller failed).
Performance may decrease for random reads and writes, but the higher areal density should offset that by a bit, and sustained reads should be close enough to the RAID'd drive to not matter much. (Writes are almost guaranteed to be slower).
So as always, it's a tradeoff sort of thing. If you already had the Seagate-branded 2x2TB unit, this wouldn't phase you at all, but for folks looking to upgrade from a smaller capacity drive, it gives them an option. Plus, this Samsung unit seems to target use with a computer only, while the Seagate-branded unit allows support of mobile devices running iOS or Android (software-based; drive must still be connected to a computer), so deciding which is better would really depend on what your needs are.