Just an update on my situation with tmobile. I have a sony xperia z1s with the $50 plan. I also have an ipad mini lte with the free 200mb plan and a Nexus 7 2013 with a free 200mb plan. At the minimum you will still need to have the $10 on demand data plan to have access to the free 200mb for the tablets but since i have a phone plan my $10 on demand plan is waived on each tablet, making my account around $56 ish a month.
Not sure what you mean by this. I have the 200mB free plan on my iPad and have no other T-Mobile accounts so I pay $0 for the 200mB.