The hell? Each standard iMac already has 1TB HDD installed. So, yes .. you pay $250 extra for 128GB SSD ONLY, which not even an actual part of the HDD itself.
It's not a hybrid drive, not some kind of customized HDD. Just one plain HDD which already installed by default, and one blade SSD, fused as one drive with built in software, not hardware. And it costs $250. So maybe you're high.
/Words matter.
One SSD drive, and software that you cannot buy anywhere else. Nobody is selling that combination cheaper. No other company actually sells it at all.