I started investing with BlockFi this year. I'd say the biggest concerns I see come up is
1) the practice of bitcoin rehypothetication
https://www.investopedia.com/terms/r/rehypothecation.asp2) The no FDIC or SIPC insurance for crypto exchanges
3) Security - exchanges get hacked all the time. Partially mitigated by turning on 2FA, whitelisting your account to limit your stash getting withdrawn to a random wallet where there's no clawback possible unlike traditional banking, and the fact that Gemini and other reputable exchanges keep most of the coins in cold storage.
4) And in general, the balance sheet strength of the company to withstand crazy price movements or other black swan event.
On the plus side, they spread out their crypto to multiple custodians, including well-respected Gemini.
With Gemini, their stablecoin GUSD is tied to USD and audited by a New York company to ensure there's no funny business. They actually have real dollars to match GUSD 1-1.
In terms of the capital stack, customers get paid 1st in the event of a catastrophic liquidation.
They are headquartered in the U.S. (I point that out because some of the other competitors are very coy about their locations & how you can contact them).
I'm not an expert on loan to asset type ratios, but it sounds like the people leading their lending program make sure their borrowers are overcollatorized and as of yet they've never had a borrower default.
To me, it seems the least shady of the numerous websites doing crypto interest accounts (Nexo & Celsius offer even higher interest rates and are often mentioned. But there are ones that seem super duper shady to me like KuCoins in Hong Kong with outrageous rates and weird fees).
In short, I'm doing it. I still want to know more about the company and listen to pretty much every podcast the CEO goes on. I suspect the rates will go down significantly when the market matures and there is less arbitrage opportunities (like the spread between exchanges and the spread between crypto futures and market price), but for the time being I've put some of the "high yield" savings account into BlockFi
EDIT: shameless plug, if anyone wants to use my referral link
https://blockfi.com/?ref=2759b0eb