don't bother with a fusion drive; its marketing more than performance.
I don't understand why many people are so down on fusion drive. Of course all SSD is better, but if you only have, or can only afford a small SSD, fusion drive works very well. I had it on my first Mac Mini, and it worked flawlessly, and 99% of the time just felt like having a 1TB SSD.
It works in a similar way to auto-tiering on an enterprise storage array, but apple bought it to the desktop and good on them. And just like what is starting to happen in enterprise arrays, fusion drive will become less relevant as SSD cost continue to come down and capacities increase, but it still provides a useful tool to meet a certain cost\performance\capacity balance.
And like all storage, whether its fusion, all SSD, or pixie dust, back up your data!