Herb has an old iMac and is thinking about getting a new iMac with the Fusion hybrid drive. Leo says that the Fusion drive will buy him a 128GB SSD with a 2-3 TB hard drive, working in concert. They work just fine. In fact, Apple's hybrid drive is better than most.
However, the speed boost from an SSD drive is lost on the fusion drive for the most part, so Leo doesn't recommend them. If speed is the issue, he should get an iMac with an SSD and then get a separate external data drive. Fusion is an overly complicated solution in his opinion.