Remember, if you are on traditional Medicare, and never had Medicare Advantage before, you may be able to try out AT&T's plan for a year and then return to the coverage you had before.
https://www.healthline.com/health/medicare/medicare-advantage-trial-period
Otherwise, if you have traditional Medicare, and try AT&T's plan, you won't be able to go back to traditional Medicare and access your Medigap (in most states¹) without underwriting, which means that the Medigap insurer will take your health condition into consideration before determining the premium, or whether they'll cover you at all.
The one thing that the HRA had was coverage for catostrophic dr-g charges, in that AT&T would reimburse your next $100,000 in prescription co-pays after you reach $5000 out-of-pocket.
Now, come 2025, there is supposed to be legislation that caps Part D at $2000, but the sky is the limit in 2024. AT&T's MAPD plan caps Part D at $6500 - no catastrophic stage. So, that coverage along with trial rights might be a one year fit. Some Part D dr-gs for cancer can run over $300,000 per year, so 5% co-pay can add up to $15,000. The HRA benefit could handle 6 of these. That $6500 cap can handle any amount of them.
¹ In Connecticut, Maine, Massachusetts, and New York, people can switch to Medigap at the annual enrollment without underwriting.