How about so-called "Brokered CDs"? If I understand them correctly, they a bank sells a large denomination CD to a brokerage company (e.g., Fidelity) who parcels chunks to individual investors. I presume the brokerage makes money several ways on this (spread, transaction, other). But somehow they smell fishy relative to just buying a vanilla CD from a bank.
Nothing fishy about it, IMO. Though I suppose like any tool it could be abused by bad people. I’ve been buying them for a few years and usually get a higher interest rate than at the banks. They have tended to beat out CDs from both my local banks and internet banks. All are FDIC insured, or I wouldn’t touch them.
Plus, I do it all with one financial business, which keeps things easy to monitor. And makes tax prep easier.
You do have to know what you are doing. I definitely recommend researching the pros and cons of brokered CDs before putting any meaningful money Into them.