US Cellular has great coverage back home (Maine) but shoddy coverage where I live now (New York) and T-Mobile vice versa. I've been on Google Fi for the past ten years because it is the only option (at least when I last looked) that jumps seamlessly between the two, and at a reasonable enough price (for a guy who doesn't use much data). If this merger makes another carrier that has good service throughout the northeast, that could change the game for a lot of customers.
I'm not optimistic, though; the T-Mobile - Sprint merger was supposed to improve their service but ended up [0] jacking their prices.