You can only buy $10k per person per year, but as a married couple, you could build up 100K in savings over 5 years, and even faster if you hold them in a trust.
One limitation of buying I Bonds is the annual purchase limit. Each person can buy a maximum of $10,000 per calendar year as the primary owner.
In addition, if you have a trust, you can buy another $10,000 per year under the name of the trust. A lawyer created a revocable living trust for us back in 2018. It was surprisingly easy when I opened an account for the trust at TreasuryDirect last month. It took only 15 minutes to open a new trust account and buy another $10,000 of I Bonds.
So it lets you double the amount you can buy.
The main benefit of cash recently is losing less value each day than stocks!