It's also potentially alluring if you like the concept of Google's pay-for-what-you-use Project Fi service but want different networks or phones. A "by the gig" option costs $12 for every gigabyte of shared data. You'll definitely be paying more than you would with Fi, but this could save some money if your household isn't big on mobile internet use.
As for device selection? It's small, but you're not getting Verizon's leftovers. Both the Galaxy S8 and iPhone 7 lineups are on tap, and the more affordable devices include older Galaxies, iPhones and LG's battery-focused Xpower. There is one catch, though: you can't currently bring your own device, so you can forget about taking your Google Pixel with you if you switch.
This is something of a gamble for Comcast. It's intentionally limiting its potential customer base, and its less-than-sterling reputation may actually deter people rather than reel them in. Still, it's hard to deny the pressure to do something on the wireless front. When rivals like AT&T are pushing their own all-inclusive offerings, Comcast likely feels that it might be leaving money on the table by making subscribers go elsewhere for phone service. And besides, this is a hedge against the future. Even if cable TV viewership tanks, Comcast could still count on customers for at least two services going forward.