I'd been with Sprint for the past 11 years so I know what to expect as far as that goes. I've been paying for unlimited data for the past several years but have only averaged .25GB/mo since I got a new job a couple years ago and I don't use it to stream music at work anymore.
I'm hoping that the T-Mobile towers will improve the somewhat spotty service that I got with Sprint sometimes. I'm interested in how seamlessly it will be able to switch from WiFi calling to using a cell tower while in mid-call.
My biggest concern is that Google, for whatever reason, will up and decide to discontinue the service (which they are known to do). Either way, I guess there are other 'pay for what you use' providers out there that I could go to if that happens.
It's bothersome that you are limited to the phones that work on it. Right now, it's basically just the Nexus 5x and 6's. Not bad phones but I would prefer a Galaxy. Also, I've never had to buy a phone without the deep discounts that you get with a 2 yr contract with the big guys. I got the 5x for $200 which is $150 off the full price. Hopefully, in the next couple years, they will bring some more phones into the fold and offer discounts on them.
All in all, it's working good after one day and the price, so far, is right.