Went to Rolling Loud NYC at Citi Field this weekend. Over 60,000 people in attendance.
Verizon is a sponsor of the festival this year so naturally they had a ton of COWs set up at the festival. I counted at least 4. As a result, they were virtually the only carrier consistently able to provide a data connection. I didn't see any Verizon 5G, only LTE.
T-Mobile on the other hand was a very interesting experience. I was seeing an eNB 331804 which I'm 99% sure is a COW. They also seems to be doing some sort of traffic management because I noticed that if I left my phone idle in my pocket, it would drop down to No Service/SOS or sometimes it would sit on EDGE. But the second that I needed to send a text, make a call, or even use Twitter my phone would switch over to LTE or 5G to complete the task. In an active data session, my phone would constantly flip between Band 2, Band 66, and Band 41. Sometimes, I'd catch myself on the COW and other times I'd get pushed over to eNB 875868, the relatively new Sprint conversion nearby. The network moved at a snails pace though. Where Verizon took about 15 seconds to load Twitter or send a pic, T-Mobile could take up to a minute to complete the same task.
Here's some photos of the COWs I spotted. I think that the first two are Verizon and the one in the distance in the third pic is T-Mobile's single COW, not nearly enough for an event that size.