It's just silly. In 2015, 200mb is basically a joke... it's T-Mo's way of boosting their net-adds to make themselves look like they're growing faster than they really are. It'd be one thing if they offered 200mb LTE as a carrot, then throttled down to HSPA after, but they don't, 200 and you're toast for the rest of the month. While people say "but it's free" ... who cares? It's like the people that line up around the block when starbucks does their free grande coffee afternoons. How much is your time worth dedicated to standing in line to get a $1.75 cup of coffee? And if 1GB of data is worth $10 including throttling unlimited once you pass it (and also includes free international roaming), I'd put a value of the 200 mb (the dies and no intl) at about $1 per month AT BEST.
It's not worth the hassle to me to even look online to see if I have any data left when I only get 200mb a month. $1 isn't worth it to me. Sorry.
Your analogy is poor. While T-Mobile's 200MB plan is a carrot to get people to sign up for paid plan or buy one-time purchase on months you go over, the fact is, there's no extra work for you to get that free 200MB monthly data for life.
I agree with terrible login experience for checking data used and purchasing additional data though.