3 things to keep in mind about nickle plated brass:
1) Due to the plating, they tend to be somewhat more brittle, so their useful "reloading life" is somewhat shorter. I tend to get split cases with less reloads. When buying, I prefer brass only - but if you can get them for free - who cares?
2) Don't leave them in the tumbler too long - will wear away on the nickle plating - if you want to maintain the shiny silver finish. However, even as the nickle starts to wear off, reloads and shoots just fine.
3) One advantage of nickle plated brass is when storing rounds in leather (holster etc.). Brass has a tendency to create a green waxy substance (exactly what it is, I don't know) when brass comes in prolonged contact with tanned leather. Something in the leather causes the reaction with brass. I never had the same problem with nickle plated brass.