I've come out actually slightly cheaper than the T-Mo plan. WIFI seems to be pretty ubiquitous where I go because I only used ~ 300MB of data last month.
Usually I use ~ 2GB per month. The one big change I did at the starting of the month was set my podcast streaming apps to sync on WIFI. That's about half of my monthly data right there.
Edit: fixed typo.
I wonder what it will be like, psychologically, when I'm paying by the megabyte for data. Right now, I know I've already paid, so I just stream stuff. Under project fi pricing, my total cost per month will go down, but it will also be metered- I can have it go way down if I'm frugal. Not sure if I'll download that audio book on LTE if I know I'm going to end up paying an extra buck for it. I mean: it's just a buck, but still. Interesting to see where I land.