Congrats on being "selected." I was too. We must be an elite group of millions.
It works pretty well, but hopefully it will improve. Perhaps they really are testing this and rolling it out to a subset of their subscribers.
I do like that backing out of one of the games returns you to the menu. That's intuitive. But the audio lag when switching the source in the grid (a few seconds) is disappointing. You can actually see a spinning indicator that it is loading. And when you switch to an individual game via the grid, the audio level is noticeably reduced. A small thing, but not as seamless as it could be.
These are minor complaints, but I did a free trial of Fubo a year ago at this time, and their multi grid was better. Theirs was user-selectable so you could choose whatever channels you wanted, and the audio switching and navigating between selections was instantaneous. I was really impressed by how well it worked.
Unfortunately, Fubo didn't have all of the Turner Networks, so this was a dealbreaker for the NCAA tournament. I switched to YouTube TV and didn't look back, but overall I think I liked Fubo's interface better. It was more polished and more intuitive. But I don't think I'd ever want to give up YouTube's unlimited recording.